diff --git a/lbplanner/classes/enums/CAPABILITY_FLAG_ORNONE.php b/lbplanner/classes/enums/CAPABILITY_FLAG_ORNONE.php
index 9a9f45cb..2e4a8f7c 100644
--- a/lbplanner/classes/enums/CAPABILITY_FLAG_ORNONE.php
+++ b/lbplanner/classes/enums/CAPABILITY_FLAG_ORNONE.php
@@ -47,8 +47,8 @@ class CAPABILITY_FLAG_ORNONE extends CAPABILITY_FLAG {
      * @link CAPABILITY
      */
     public static function to_capability(int $num): string {
-        if ($num === 0) { // TODO: put in translation strings.
-            throw new \coding_exception('0 means the absence of capabilities, and thus cannot be converted to a capability');
+        if ($num === 0) {
+            throw new \coding_exception(get_string('err_enum_capability_none', 'local_lbplanner'));
         }
         return parent::to_capability($num);
     }
diff --git a/lbplanner/classes/helpers/config_helper.php b/lbplanner/classes/helpers/config_helper.php
index b2b63343..9980f49a 100644
--- a/lbplanner/classes/helpers/config_helper.php
+++ b/lbplanner/classes/helpers/config_helper.php
@@ -53,8 +53,8 @@ public static function add_customfield(): void {
 
                 $fieldcontroller = field_controller::create(0, $record, $categorycontroller);
                 // Added the default attributes for the custom field.
-                $fieldcontroller->set('name', 'LB Planer Task Type');
-                $fieldcontroller->set('description', 'Tracks whether the task is GK/EK/TEST/M');
+                $fieldcontroller->set('name', get_string('cf_name', 'local_lbplanner'));
+                $fieldcontroller->set('description', get_string('cf_description', 'local_lbplanner'));
                 $fieldcontroller->set('type', 'select');
                 // Because moodle wants me to save the configdata as a json string, I have to do this.
                 // I don't know why moodle does this, but it does. I don't like it. but I have to do it. so I do it.
diff --git a/lbplanner/classes/helpers/invite_helper.php b/lbplanner/classes/helpers/invite_helper.php
index 919f5819..288e9939 100644
--- a/lbplanner/classes/helpers/invite_helper.php
+++ b/lbplanner/classes/helpers/invite_helper.php
@@ -54,7 +54,8 @@ public static function structure(): external_single_structure {
     public static function assert_invite_pending(int $status) {
         if ($status !== PLAN_INVITE_STATE::PENDING) {
             $name = PLAN_INVITE_STATE::name_from($status);
-            throw new \moodle_exception("Invite already {$name}");
+            $translatedname = get_string('invite_state_' . strtolower($name), 'local_lbplanner');
+            throw new \moodle_exception(get_string('err_invite_alr', 'local_lbplanner', $translatedname));
         }
     }
 }
diff --git a/lbplanner/classes/helpers/modules_helper.php b/lbplanner/classes/helpers/modules_helper.php
index 6660d6e6..3b01d33f 100644
--- a/lbplanner/classes/helpers/modules_helper.php
+++ b/lbplanner/classes/helpers/modules_helper.php
@@ -125,16 +125,17 @@ public static function determine_uinified_grade(int $grade, int $maxgrade, int $
      * @throws \moodle_exception
      */
     public static function determine_type(int $cmid): int {
+        // TODO: cache category controller.
         $catid = config_helper::get_category_id();
         if ($catid === -1) {
-            throw new \moodle_exception('couldn\'t find custom fields category ID');
+            throw new \moodle_exception(get_string('err_cf_nocatid', 'local_lbplanner'));
         }
         $categorycontroller = category_controller::create($catid);
         $instancedata = $categorycontroller->get_handler()->get_instance_data($cmid);
         if (count($instancedata) === 0) {
-            throw new \moodle_exception("couldn't find any instance data for module ID {$cmid} in category ID {$catid}");
+            throw new \moodle_exception(get_string('err_cf_nodata', 'local_lbplanner', ['cmid' => $cmid, 'catid' => $catid]));
         } else if (count($instancedata) > 1) {
-            throw new \moodle_exception("found multiple data for module ID {$cmid} in category ID {$catid}");
+            throw new \moodle_exception(get_string('err_cf_multidata', 'local_lbplanner', ['cmid' => $cmid, 'catid' => $catid]));
         }
         $type = intval($instancedata[array_key_last($instancedata)]->get_value()) - 1;
         if ($type === -1) {
diff --git a/lbplanner/classes/helpers/plan_helper.php b/lbplanner/classes/helpers/plan_helper.php
index fa82bb1f..e47036be 100644
--- a/lbplanner/classes/helpers/plan_helper.php
+++ b/lbplanner/classes/helpers/plan_helper.php
@@ -261,19 +261,19 @@ public static function copy_plan(int $planid, string $username): int {
     public static function remove_user(int $planid, int $userid, int $removeuserid): int {
         global $DB; // TODO: use global user object.
         if (self::get_owner($planid) != $userid) {
-            throw new \moodle_exception('Access denied');
+            throw new \moodle_exception(get_string('err_accessdenied', 'local_lbplanner'));
         }
 
         if (self::get_plan_id($removeuserid) != $planid) {
-            throw new \moodle_exception('Cannot remove user from other plan');
+            throw new \moodle_exception(get_string('err_plan_cantremove_userfromother', 'local_lbplanner'));
         }
 
         if ($userid == $removeuserid) {
-            throw new \moodle_exception('Cannot remove yourself');
+            throw new \moodle_exception(get_string('err_plan_cantremove_yourself', 'local_lbplanner'));
         }
 
         if (self::get_access_type($removeuserid, $planid) === PLAN_ACCESS_TYPE::OWNER) {
-            throw new \moodle_exception('Cannot remove owner');
+            throw new \moodle_exception(get_string('err_plan_cantremove_owner', 'local_lbplanner'));
         }
 
         $newplanid = self::copy_plan($planid, user_helper::get_mdluser($removeuserid)->username);
diff --git a/lbplanner/classes/helpers/sentry_helper.php b/lbplanner/classes/helpers/sentry_helper.php
index a796b407..75a95aec 100644
--- a/lbplanner/classes/helpers/sentry_helper.php
+++ b/lbplanner/classes/helpers/sentry_helper.php
@@ -89,7 +89,7 @@ public static function init(): void {
     public static function transaction_start(string $name, string $op, ?array $data = null): ?Transaction {
         if (self::enabled()) {
             if (SentrySdk::getCurrentHub()->getSpan() !== null) {
-                throw new \coding_exception('tried to start a new sentry transaction when there\'s already a span set');
+                throw new \coding_exception(get_string('err_sentry_transactcoll', 'local_lbplanner'));
             }
             $ctx = TransactionContext::make()
                 ->setName($name)
diff --git a/lbplanner/classes/helpers/slot_helper.php b/lbplanner/classes/helpers/slot_helper.php
index 8d77d0bc..70a52e98 100644
--- a/lbplanner/classes/helpers/slot_helper.php
+++ b/lbplanner/classes/helpers/slot_helper.php
@@ -219,7 +219,7 @@ public static function get_reservation(int $reservationid): reservation {
         $reservation = $DB->get_record(self::TABLE_RESERVATIONS, ['id' => $reservationid]);
 
         if ($reservation === false) {
-            throw new \moodle_exception('requested reservation does not exist');
+            throw new \moodle_exception(get_string('err_slot_reservnoexist', 'local_lbplanner', $reservationid));
         }
 
         return reservation::from_obj($reservation);
@@ -395,7 +395,7 @@ public static function calculate_slot_datetime(slot $slot, DateTimeImmutable $no
         // Move to next day this weekday occurs (doesn't move if it's the same as today).
         $slotdatetime = $now->modify('this ' . WEEKDAY::name_from($slot->weekday) . " {$slotdaytime}");
         if ($slotdatetime === false) {
-            throw new \coding_exception('error while calculating slot datetime');
+            throw new \coding_exception(get_string('err_slot_calcdatetime', 'local_lbplanner'));
         }
 
         // Check if slot is before now (because time of day and such) and move it a week into the future if so.
@@ -449,7 +449,7 @@ public static function check_slot_supervisor(int $supervisorid, int $slotid): bo
      */
     public static function assert_slot_supervisor(int $supervisorid, int $slotid): void {
         if (!self::check_slot_supervisor($supervisorid, $slotid)) {
-            throw new \moodle_exception('Insufficient Permission: you\'re not supervisor of this slot');
+            throw new \moodle_exception(get_string('err_slot_urnotsupervisor', 'local_lbplanner'));
         }
     }
 }
diff --git a/lbplanner/classes/helpers/user_helper.php b/lbplanner/classes/helpers/user_helper.php
index abd3fb20..18838ab7 100644
--- a/lbplanner/classes/helpers/user_helper.php
+++ b/lbplanner/classes/helpers/user_helper.php
@@ -79,7 +79,7 @@ public static function get_user(int $userid): user {
 
         // Create empty plan for newly registered user.
         $plan = new \stdClass();
-        $plan->name = 'Plan for ' . ($eduplanneruser->get_mdluser()->username);
+        $plan->name = get_string('plan_defaultname', 'local_lbplanner', $eduplanneruser->get_mdluser()->username);
         $planid = $DB->insert_record(plan_helper::TABLE, $plan);
         $eduplanneruser->set_planid($planid);
 
diff --git a/lbplanner/classes/model/course.php b/lbplanner/classes/model/course.php
index b0c09d61..da3a8f32 100644
--- a/lbplanner/classes/model/course.php
+++ b/lbplanner/classes/model/course.php
@@ -71,6 +71,7 @@ class course {
      * @param bool $enabled whether the course is enabled
      */
     public function __construct(int $id, int $courseid, int $userid, string $shortname, string $color, bool $enabled) {
+        // TODO: private constructor, remove checks, separate public function with checks.
         $this->id = $id;
         $this->courseid = $courseid;
         $this->userid = $userid;
@@ -110,7 +111,7 @@ public function set_fresh(int $id) {
      */
     public function set_color(string $color) {
         if ($color[0] !== '#') {
-            throw new \coding_exception("incorrect color format - must be either #RGB or #RRGGBB, got \"{$color}\" instead");
+            throw new \coding_exception(get_string('err_color_wrongformat', 'local_lbplanner', $color));
         }
         $len = strlen($color);
         if ($len === 4) {
@@ -122,11 +123,11 @@ public function set_color(string $color) {
             // Format #RRGGBB.
             $rrggbb = $color;
         } else {
-            throw new \coding_exception("incorrect color format - got incorrect length of {$len}");
+            throw new \coding_exception(get_string('err_color_wronglength', 'local_lbplanner', $len));
         }
         $rrggbb = strtoupper($rrggbb);
         if (preg_match('/^#[1-9A-F]{6}$/', $rrggbb) === false) {
-            throw new \coding_exception("incorrect color format - found non-hexadecimal character in color \"{$color}\"");
+            throw new \coding_exception(get_string('err_color_nonhexadecimal', 'local_lbplanner', $color));
         }
         $this->color = $rrggbb;
     }
@@ -139,7 +140,7 @@ public function set_color(string $color) {
     public function set_shortname(string $shortname) {
         $length = strlen($shortname);
         if ($length > 5 || $length < 0) {
-            throw new \moodle_exception("shortname length must be <=5 and >0, but is {$length} instead");
+            throw new \moodle_exception(get_string('err_course_shortnamelength', 'local_lbplanner', $length));
         }
         $this->shortname = $shortname;
     }
@@ -173,7 +174,7 @@ public static function prepare_shortname(string $shortname): string {
      */
     public function set_mdlcourse(\stdClass $mdlcourse): void {
         if ($this->mdlcourse !== null) {
-            throw new \coding_exception('tried to set cached mdluser twice');
+            throw new \coding_exception(get_string('err_doublechacheset', 'local_lbplanner', 'mdlcourse'));
         }
         $this->mdlcourse = $mdlcourse;
     }
diff --git a/lbplanner/classes/model/module.php b/lbplanner/classes/model/module.php
index a6c6c62a..6384810e 100644
--- a/lbplanner/classes/model/module.php
+++ b/lbplanner/classes/model/module.php
@@ -139,7 +139,7 @@ public function get_assignid(): int {
             if ($this->cmid !== null) {
                 $this->assignid = $this->get_cmobj()->instance;
             } else {
-                throw new \coding_exception('requested assignid, but no cmid');
+                throw new \coding_exception(get_string('err_mod_assnocmid', 'local_lbplanner'));
             }
         }
         return $this->assignid;
@@ -185,11 +185,11 @@ public function get_cmobj(): \stdClass {
                     ['id' => $this->cmid, 'module' => modules_helper::get_assign_module_id()]
                 );
                 if ($res === false) {
-                    throw new \moodle_exception("couldn't get course module with cmid {$this->cmid}");
+                    throw new \moodle_exception(get_string('err_mod_cmidnocm', 'local_lbplanner', $this->cmid));
                 }
             } else {
                 if ($this->assignid === null) {
-                    throw new \coding_exception('tried to query cmid on a module object without assignid');
+                    throw new \coding_exception(get_string('err_mod_cmidnoass', 'local_lbplanner'));
                 }
                 $courseid = $this->get_courseid();
                 $res = $DB->get_record(
@@ -201,9 +201,11 @@ public function get_cmobj(): \stdClass {
                     ]
                 );
                 if ($res === false) {
-                    throw new \moodle_exception(
-                        "couldn't get course module with assignid {$this->assignid} and courseid {$courseid}"
-                    );
+                    throw new \moodle_exception(get_string(
+                        'err_mod_assnocm',
+                        'local_lbplanner',
+                        ['assignid' => $this->assignid, 'courseid' => $courseid],
+                    ));
                 }
             }
             $this->cmobj = $res;
@@ -243,7 +245,7 @@ public function get_courseid(): int {
                 if ($this->cmid !== null) {
                     $viacm = true;
                 } else if ($this->cmid === null) {
-                    throw new \coding_exception('invalid module model: neither cmid nor assignid defined');
+                    throw new \coding_exception(get_string('err_mod_nocmidnorass', 'local_lbplanner'));
                 }
             }
         }
diff --git a/lbplanner/classes/model/slot.php b/lbplanner/classes/model/slot.php
index c2816a53..53f2b0de 100644
--- a/lbplanner/classes/model/slot.php
+++ b/lbplanner/classes/model/slot.php
@@ -88,40 +88,16 @@ class slot {
      */
     public function __construct(int $id, int $startunit, int $duration, int $weekday, string $room, int $size) {
         $this->id = $id;
-        if ($startunit <= 0 || $startunit > slot_helper::SCHOOL_UNIT_MAX) {
-            throw new \moodle_exception(
-                "slot's startunit must be >0 and <="
-                . slot_helper::SCHOOL_UNIT_MAX
-                . ", but is {$startunit}"
-            );
-        }
-        if ($duration <= 0 || ($startunit + $duration - 1) > slot_helper::SCHOOL_UNIT_MAX) {
-            throw new \moodle_exception(
-                "slot's duration must be >0 and can't exceed "
-                . slot_helper::SCHOOL_UNIT_MAX
-                . " with startunit, but is {$duration}"
-            );
-        }
         $this->startunit = $startunit;
         $this->duration = $duration;
         $this->weekday = WEEKDAY::from($weekday);
-        if (strlen($room) <= 0 && strlen($room) > slot_helper::ROOM_MAXLENGTH) {
-            throw new \moodle_exception(
-                "room name's length must be >0 and <="
-                . slot_helper::ROOM_MAXLENGTH
-                . ", but is "
-                . strlen($room)
-            );
-        }
         $this->room = $room;
-        if ($size < 0) {
-            throw new \moodle_exception('room size must be >0');
-        }
         $this->size = $size;
         $this->fullness = null;
         $this->forcuruser = null;
         $this->supervisors = null;
         $this->filters = null;
+        $this->validate();
     }
 
     /**
@@ -161,27 +137,29 @@ public function validate(): void {
         static $maxunit = slot_helper::SCHOOL_UNIT_MAX;
          // Validating startunit.
         if ($this->startunit < 1) {
-            throw new moodle_exception('can\'t have a start unit smaller than 1');
+            throw new moodle_exception(get_string('err_slot_startunittoosmall', 'local_lbplanner'));
         } else if ($this->startunit > $maxunit) {
-            throw new moodle_exception("can't have a start unit larger than {$maxunit}");
+            throw new moodle_exception(get_string('err_slot_startunittoolarge', 'local_lbplanner'));
         }
         // Validating duration.
         if ($this->duration < 1) {
-            throw new moodle_exception('duration must be at least 1');
+            throw new moodle_exception(get_string('err_slot_durationtoosmall', 'local_lbplanner'));
         } else if ($this->startunit + $this->duration > $maxunit) {
-            throw new moodle_exception("slot goes past the max unit {$maxunit}");
+            throw new moodle_exception(get_string('err_slot_durationtoolarge', 'local_lbplanner', $maxunit));
         }
         // Validating weekday.
         WEEKDAY::from($this->weekday);
         // Validating room.
         if (strlen($this->room) <= 1) {
-            throw new moodle_exception('room name has to be at least 2 characters long');
+            throw new moodle_exception(get_string('err_slot_roomnametooshort', 'local_lbplanner'));
         } else if (strlen($this->room) > slot_helper::ROOM_MAXLENGTH) {
-            throw new moodle_exception('room name has a maximum of ' . slot_helper::ROOM_MAXLENGTH . ' characters');
+            throw new moodle_exception(
+                get_string('err_slot_roomnametoolong', 'local_lbplanner', slot_helper::ROOM_MAXLENGTH)
+            );
         }
         // Validating size.
         if ($this->size < 0) {
-            throw new moodle_exception('can\'t have a negative size for a slot');
+            throw new moodle_exception(get_string('err_slot_roomsizetoosmall', 'local_lbplanner'));
         }
     }
 
diff --git a/lbplanner/classes/model/slot_filter.php b/lbplanner/classes/model/slot_filter.php
index ca16b065..d9f17caf 100644
--- a/lbplanner/classes/model/slot_filter.php
+++ b/lbplanner/classes/model/slot_filter.php
@@ -58,6 +58,11 @@ class slot_filter {
     public function __construct(int $id, int $slotid, int $courseid, string $vintage) {
         assert(strlen($vintage) <= 7);
 
+        // Ensure that either $courseid or $vintage are non-null.
+        if (is_null($courseid) && is_null($vintage)) {
+            throw new \moodle_exception(get_string('err_slotfilter_bothnull', 'local_lbplanner'));
+        }
+
         $this->id = $id;
         $this->slotid = $slotid;
         $this->courseid = $courseid;
diff --git a/lbplanner/classes/model/user.php b/lbplanner/classes/model/user.php
index 1b2157b4..80fc10fe 100644
--- a/lbplanner/classes/model/user.php
+++ b/lbplanner/classes/model/user.php
@@ -240,7 +240,7 @@ public function set_mdluser(\stdClass $mdluser): void {
         global $USER;
         if ($this->mdluser !== null) {
             if ($this->mdluser->id !== $USER->id) {
-                throw new \coding_exception('tried to set cached mdluser twice');
+                throw new \coding_exception(get_string('err_doublechacheset', 'local_lbplanner', 'mdluser'));
             }
         }
         $this->mdluser = $mdluser;
@@ -264,7 +264,7 @@ public function get_mdluser(): \stdClass {
      */
     public function set_planid(int $planid): void {
         if ($this->planid !== null) {
-            throw new \coding_exception('tried to set cached planid twice');
+            throw new \coding_exception(get_string('err_doublechacheset', 'local_lbplanner', 'planid'));
         }
         $this->planid = $planid;
     }
diff --git a/lbplanner/classes/polyfill/Enum.php b/lbplanner/classes/polyfill/Enum.php
index bdf49e46..ee84d45a 100644
--- a/lbplanner/classes/polyfill/Enum.php
+++ b/lbplanner/classes/polyfill/Enum.php
@@ -70,7 +70,9 @@ private static function find_from_name(string $name, bool $try): ?EnumCase {
         if ($try) {
             return null;
         } else {
-            throw new \moodle_exception("name {$name} doesn't exist in " . static::class);
+            throw new \moodle_exception(
+                get_string('err_enum_namemissing', 'local_lbplanner', ['name' => $name, 'classname' => static::class])
+            );
         }
     }
     /**
@@ -163,7 +165,7 @@ public static function format(): string {
             } else if (is_int($case->value)) {
                 $formattedval = $case->value;
             } else {
-                throw new moodle_exception('unimplemented case value type for Enum::format()');
+                throw new moodle_exception(get_string('err_enum_casevaluetype_unimp', 'local_lbplanner'));
             }
             $result .= "{$formattedval}=>{$case->name},";
         }
diff --git a/lbplanner/db/access.php b/lbplanner/db/access.php
index 9de3ea5e..db76118c 100644
--- a/lbplanner/db/access.php
+++ b/lbplanner/db/access.php
@@ -45,9 +45,9 @@
 
 $deprecatedcapabilities = [
     'local/lb_planner:admin' => [
-        'message' => 'this capability was removed because of internal changes making it unnecessary',
+        'message' => get_string('capability_deprecated_unnecessary', 'local_lbplanner'),
     ],
     'local/lb_planner:manager' => [
-        'message' => 'this capability was removed because of internal changes making it unnecessary',
+        'message' => get_string('capability_deprecated_unnecessary', 'local_lbplanner'),
     ],
 ];
diff --git a/lbplanner/lang/de/local_lbplanner.php b/lbplanner/lang/de/local_lbplanner.php
new file mode 100644
index 00000000..60e4b96e
--- /dev/null
+++ b/lbplanner/lang/de/local_lbplanner.php
@@ -0,0 +1,109 @@
+<?php
+// This file is part of the local_lbplanner.
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Defines some translation strings in german.
+ *
+ * @package local_lbplanner
+ * @copyright 2025 Pallasys
+ * @license https://creativecommons.org/licenses/by-nc-sa/4.0/ CC-BY-NC-SA 4.0 International or later
+ */
+
+defined('MOODLE_INTERNAL') || die();
+
+$string['capability_deprecated_unnecessary'] = 'Diese Berechtigung wurde entfernt, da sie nicht mehr benötigt wird';
+$string['cf_description'] = 'Gibt an, ob die Aufgabe GK/EK/TEST/M ist';
+$string['cf_name'] = 'LB Planer Aufgabentyp';
+$string['err_accessdenied'] = 'Zugriff verweigert';
+$string['err_cf_multidata'] = 'Mehrere Einträge für Modul-ID {$a->cmid} in Kategorie-ID {$a->catid}';
+$string['err_cf_nocatid'] = 'Kategorie-ID für Custom Fields nicht gefunden';
+$string['err_cf_nodata'] = 'Keine Instanzdaten für Modul-ID {$a->cmid} in Kategorie-ID {$a->catid}';
+$string['err_color_nonhexadecimal'] = 'Ungültiges Farbformat - nicht-hexadezimalziffer in "{$a}"';
+$string['err_color_wrongformat'] = 'Ungültiges Farbformat - erwartet #RGB oder #RRGGBB, nicht "{$a}"';
+$string['err_color_wronglength'] = 'Ungültiges Farbformat - falsche Länge von {$a}';
+$string['err_course_shortnamelength'] = 'Länge des Kurznamens muss <=5 und >0 sein (aktuell: {$a})';
+$string['err_dateformat'] = 'Ungültiges Datumsformat: \'{$a}\' erhalten, erwartet YYYY-MM-DD';
+$string['err_doublechacheset'] = 'Versuchte {$a} doppelt im Cache zu speichern';
+$string['err_enum_capability_none'] =
+    '0 heißt die Abwesenheit von Berechtigungen, und kann daher nicht zur Berechtigung umgewandelt werden';
+$string['err_enum_casevaluetype_unimp'] = 'Nicht implementierter Case Value Typ für Enum::format()';
+$string['err_enum_namemissing'] = 'Name {$a->name} existiert nicht in {$a->classname}';
+$string['err_invite_alr'] = 'Einladung bereits {$a}';
+$string['err_invite_alrinvited'] = 'Kann keineN NutzerIn einladen dier bereits eingeladen wurde';
+$string['err_invite_alrmember'] = 'Kann keineN NutzerIn einladen dier bereits Mitglied ist';
+$string['err_invite_notfound'] = 'Einladung existiert nicht';
+$string['err_invite_yourself'] = 'Kann dich nicht selbst einladen';
+$string['err_mod_assnocm'] = 'Kursmodul mit assignid {$a->assignid} und courseid {$a->courseid} konnte nicht abgerufen werden';
+$string['err_mod_assnocmid'] = 'assignid angefordert, aber keine cmid gesetzt';
+$string['err_mod_cmidnoass'] = 'cmid angefordert, aber keine assignid gesetzt';
+$string['err_mod_cmidnocm'] = 'Kursmodul mit cmid {$a} konnte nicht abgerufen werden';
+$string['err_mod_nocmidnorass'] = 'Ungültiges Modulmodell: weder cmid noch assignid gesetzt';
+$string['err_notif_notfound'] = 'Benachrichtigung nicht gefunden';
+$string['err_panic'] = 'PANIK';
+$string['err_plan_cantleave_empty'] = 'Kann Plan nicht austreten: Plan muss mindestens ein weiteres Mitglied haben';
+$string['err_plan_cantremove_owner'] = 'Kann BesitzerIn nicht entfernen';
+$string['err_plan_cantremove_userfromother'] = 'Kann keineN NutzerIn von einem Plan entfernen in dem sier nicht ist';
+$string['err_plan_cantremove_yourself'] = 'Kann dich nicht selbst entfernen';
+$string['err_plan_changeaccess_inval'] = 'Ungültiger Zugriffstyp';
+$string['err_plan_changeaccess_ofowner'] = 'Kann Berechtigungen ders BesitzerIns nicht ändern';
+$string['err_plan_changeaccess_self'] = 'Kann eigene Berechtigungen nicht ändern';
+$string['err_plan_changeaccess_toowner'] = 'Kann Berechtigungen nicht auf BesitzerIn ändern';
+$string['err_reserv_past'] = 'Vergangene Termine können nicht reserviert werden';
+$string['err_reserv_slotfull'] = 'Slot ist schon voll';
+$string['err_reserv_studentalrin'] = 'SchülerIn hat bereits eine Reservierung für diesen Slot';
+$string['err_reserv_studentnoaccess'] = 'SchülerIn hat keinen Zugriff auf diesen Slot';
+$string['err_reserv_toofuture'] = 'Datum ist nach erlaubten Datum ({$a} Tage in der Zukunft)';
+$string['err_reserv_unreserv_alrended'] = 'Kann bereits vergangene Reservierung nicht stornieren';
+$string['err_reserv_unreserv_alrstarted'] = 'Kann bereits begonnene Reservierung nicht stornieren';
+$string['err_reserv_unreserv_alrstartedorforce'] =
+    'Schüler können bereits begonnene Reservierungen nicht stornieren. Falls du trotzdem stornieren willst, bitte erzwingen.';
+$string['err_sentry_transactcoll'] = 'Versuchte neue Sentry-Transaktion zu starten obwohl ein Span schon existiert';
+$string['err_sentry_webservfalse'] = 'Webservice-Override: call_user_func_array gab bei {$a} false zurück';
+$string['err_slot_calcdatetime'] = 'Slot-Zeitpunkt konnte nicht berechnet werden';
+$string['err_slot_durationtoolarge'] = 'Slot-Starteinheit plus Dauer muss <={$a} sein';
+$string['err_slot_durationtoosmall'] = 'Slot-Dauer muss >=1 sein';
+$string['err_slot_overfull'] = 'Slot ist jetzt überfüllt';
+$string['err_slot_reservnoexist'] = 'Reservierung {$a} existiert nicht';
+$string['err_slot_roomnametoolong'] = 'Raumname darf maximal {$a} Zeichen haben';
+$string['err_slot_roomnametooshort'] = 'Raumname muss mindestens 2 Zeichen haben';
+$string['err_slot_roomsizetoosmall'] = 'Raumgröße muss >=0 sein';
+$string['err_slot_startunittoolarge'] = 'Slot-Starteinheit muss <={$a} sein';
+$string['err_slot_startunittoosmall'] = 'Slot-Starteinheit muss >=1 sein';
+$string['err_slot_urnotsupervisor'] = 'Du bist kein Betreuer dieses Slots';
+$string['err_slotfilter_bothnull'] = 'courseid und vintage können nicht beide null sein';
+$string['err_user_notfound'] = 'NutzerIn nicht in EduPlanner registriert';
+$string['invite_state_accepted'] = 'akzeptiert';
+$string['invite_state_declined'] = 'abgelehnt';
+$string['invite_state_expired'] = 'abgelaufen';
+$string['invite_state_pending'] = 'ausstehend';
+$string['lb_planner:admin'] = 'LB Planner Admin';
+$string['lb_planner:manager'] = 'LB Planner ManagerIn';
+$string['lb_planner:slotmaster'] = 'LB Planner Slotmeister';
+$string['lb_planner:student'] = 'LB Planner SchülerIn';
+$string['lb_planner:teacher'] = 'LB Planner Lehrkraft';
+$string['plan_defaultname'] = 'Plan für {$a}';
+$string['pluginname'] = 'LB Planner';
+$string['sett_futuresight_desc'] = 'Wie viele Tage im Voraus Schüler Termine/Slots buchen dürfen. (0 = nur selber Tag)';
+$string['sett_futuresight_title'] = 'Reservierungszeitraum der Schüler';
+$string['sett_outdaterange_desc'] = 'Die maximale Dauer, die ein Kurs nach seinem Ende im EduPlanner sichtbar bleibt.';
+$string['sett_outdaterange_title'] = 'Sichtbarkeitsdauer nach Kursende';
+$string['sett_panic_desc'] =
+    'Schaltet API ab - nur im Notfall. Kein Datenverlust, aber totale Abschaltung der Dienste bis die box enthakt wird.';
+$string['sett_panic_title'] = 'PANIKSCHALTER';
+$string['sett_sentrydsn_desc'] = 'Wo Fehlermeldungen hingeschickt werden. (Bitte frag das Pallasys-Team um einen Code)';
+$string['sett_sentrydsn_title'] = 'Sentry DSN';
+$string['unit_day'] = 'Tag';
+$string['unit_day_pl'] = 'Tage';
diff --git a/lbplanner/lang/en/local_lbplanner.php b/lbplanner/lang/en/local_lbplanner.php
index 07fceb43..d7173fcf 100644
--- a/lbplanner/lang/en/local_lbplanner.php
+++ b/lbplanner/lang/en/local_lbplanner.php
@@ -15,7 +15,7 @@
 // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
 
 /**
- * Defines some translation strings in english
+ * Defines some translation strings in english.
  *
  * @package local_lbplanner
  * @copyright 2025 Pallasys
@@ -24,8 +24,86 @@
 
 defined('MOODLE_INTERNAL') || die();
 
+$string['capability_deprecated_unnecessary'] = 'This capability was removed because of internal changes making it unnecessary';
+$string['cf_description'] = 'Tracks whether the task is GK/EK/TEST/M';
+$string['cf_name'] = 'LB Planer Task Type';
+$string['err_accessdenied'] = 'Access denied';
+$string['err_cf_multidata'] = 'Found multiple data for module ID {$a->cmid} in category ID {$a->catid}';
+$string['err_cf_nocatid'] = 'Couldn\'t find custom fields category ID';
+$string['err_cf_nodata'] = 'Couldn\'t find any instance data for module ID {$a->cmid} in category ID {$a->catid}';
+$string['err_color_nonhexadecimal'] = 'Incorrect color format - found non-hexadecimal character in color "{$a}"';
+$string['err_color_wrongformat'] = 'Incorrect color format - must be either #RGB or #RRGGBB, got "{$a}" instead';
+$string['err_color_wronglength'] = 'Incorrect color format - got incorrect length of {$a}';
+$string['err_course_shortnamelength'] = 'Shortname length must be <=5 and >0, but is {$a} instead';
+$string['err_dateformat'] = 'Invalid date formatting: got \'{$a}\', must be YYYY-MM-DD';
+$string['err_doublechacheset'] = 'Tried to set cached {$a} twice';
+$string['err_enum_capability_none'] =
+    '0 means the absence of capabilities, and thus cannot be converted to a capability';
+$string['err_enum_casevaluetype_unimp'] = 'Unimplemented case value type for Enum::format()';
+$string['err_enum_namemissing'] = 'Name {$a->name} doesn\'t exist in {$a->classname}';
+$string['err_invite_alr'] = 'Invite already {$a}';
+$string['err_invite_alrinvited'] = 'Cannot invite user who is already been invited';
+$string['err_invite_alrmember'] = 'Cannot invite user who is already a member';
+$string['err_invite_notfound'] = 'Invitation does not exist';
+$string['err_invite_yourself'] = 'Cannot invite yourself';
+$string['err_mod_assnocm'] = 'Couldn\'t get course module with assignid {$a->assignid} and courseid {$a->courseid}';
+$string['err_mod_assnocmid'] = 'Requested assignid, but no cmid is set';
+$string['err_mod_cmidnoass'] = 'Requested cmid, but no assignid is set';
+$string['err_mod_cmidnocm'] = 'Couldn\'t get course module with cmid {$a}';
+$string['err_mod_nocmidnorass'] = 'Invalid module model: neither cmid nor assignid defined';
+$string['err_notif_notfound'] = 'Notification does not exist';
+$string['err_panic'] = 'PANIC';
+$string['err_plan_cantleave_empty'] = 'Cannot Leave Plan: Plan must have at least one other member';
+$string['err_plan_cantremove_owner'] = 'Cannot remove owner';
+$string['err_plan_cantremove_userfromother'] = 'Cannot remove user from a plan they aren\'t in';
+$string['err_plan_cantremove_yourself'] = 'Cannot remove yourself';
+$string['err_plan_changeaccess_inval'] = 'Access type not valid';
+$string['err_plan_changeaccess_ofowner'] = 'Cannot change permissions for the plan owner';
+$string['err_plan_changeaccess_self'] = 'Cannot change own permissions';
+$string['err_plan_changeaccess_toowner'] = 'Cannot change permission to owner';
+$string['err_reserv_past'] = 'Can\'t reserve date in the past';
+$string['err_reserv_slotfull'] = 'Slot is already full';
+$string['err_reserv_studentalrin'] = 'Student already has a reservation for this slot';
+$string['err_reserv_studentnoaccess'] = 'Student does not have access to this slot';
+$string['err_reserv_toofuture'] = 'Date is past allowed date ({$a} days in the future)';
+$string['err_reserv_unreserv_alrended'] = 'You can\'t unbook this reservation because it has already ended';
+$string['err_reserv_unreserv_alrstarted'] = 'You can\'t unbook this reservation because it has already started';
+$string['err_reserv_unreserv_alrstartedorforce'] =
+    'Students can\'t unbook reservations that have already started. If you want to unbook this reservation regardless, force it.';
+$string['err_sentry_transactcoll'] = 'Tried to start a new sentry transaction when there\'s already a span set';
+$string['err_sentry_webservfalse'] = 'Webservice override: call_user_func_array returned with false at {$a}';
+$string['err_slot_calcdatetime'] = 'Could not calculate slot datetime';
+$string['err_slot_durationtoolarge'] = 'Slot start unit plus duration must be <={$a}';
+$string['err_slot_durationtoosmall'] = 'Slot duration must be >=1';
+$string['err_slot_overfull'] = 'Slot is now overfull';
+$string['err_slot_reservnoexist'] = 'Reservation {$a} does not exist';
+$string['err_slot_roomnametoolong'] = 'Room name has to be {$a} characters long or shorter';
+$string['err_slot_roomnametooshort'] = 'Room name has to be at least 2 characters long';
+$string['err_slot_roomsizetoosmall'] = 'Room size must be >=0';
+$string['err_slot_startunittoolarge'] = 'Slot start unit must be <={$a}';
+$string['err_slot_startunittoosmall'] = 'Slot start unit must be >=1';
+$string['err_slot_urnotsupervisor'] = 'Insufficient Permission: you\'re not supervisor of this slot';
+$string['err_slotfilter_bothnull'] = 'Courseid and vintage can\'t both be null';
+$string['err_user_notfound'] = 'User is not registered in Eduplanner';
+$string['invite_state_accepted'] = 'accepted';
+$string['invite_state_declined'] = 'declined';
+$string['invite_state_expired'] = 'expired';
+$string['invite_state_pending'] = 'pending';
 $string['lb_planner:admin'] = 'LB Planner Admin';
 $string['lb_planner:manager'] = 'LB Planner Manager';
+$string['lb_planner:slotmaster'] = 'LB Planner Slotmaster';
 $string['lb_planner:student'] = 'LB Planner Student';
 $string['lb_planner:teacher'] = 'LB Planner Teacher';
+$string['plan_defaultname'] = 'Plan for {$a}';
 $string['pluginname'] = 'LB Planner';
+$string['sett_futuresight_desc'] = 'Maximum number of days in advance students can reserve slots. (0 = same day only)';
+$string['sett_futuresight_title'] = 'Students\' reservation range';
+$string['sett_outdaterange_desc'] = 'The maximum duration a course remains visible in EduPlanner after it ends.';
+$string['sett_outdaterange_title'] = 'Courses\' outdated range';
+$string['sett_panic_desc'] =
+    'Turns API off - only use in emergencies. No data loss, but total loss of EduPlanner services until box is unchecked.';
+$string['sett_panic_title'] = 'PANIC SWITCH';
+$string['sett_sentrydsn_desc'] = 'For where to send error debugging info to. (Please ask the Pallasys team for a key)';
+$string['sett_sentrydsn_title'] = 'Sentry DSN';
+$string['unit_day'] = 'Day';
+$string['unit_day_pl'] = 'Days';
diff --git a/lbplanner/lib.php b/lbplanner/lib.php
index 59b097bd..c90809f8 100644
--- a/lbplanner/lib.php
+++ b/lbplanner/lib.php
@@ -36,7 +36,7 @@ function local_lbplanner_override_webservice_execution(stdClass $externalfunctio
     // Only override calling our own functions.
     if ($externalfunctioninfo->component === 'local_lbplanner') {
         if (get_config('local_lbplanner', SETTINGS::PANIC) === '1') {
-            throw new \moodle_exception('PANIC'); // TODO: add to translations.
+            throw new \moodle_exception(get_string('err_panic', 'local_lbplanner'));
         }
         sentry_helper::init();
         // Actually calling the function (since we're overriding this part, duh).
@@ -49,15 +49,8 @@ function local_lbplanner_override_webservice_execution(stdClass $externalfunctio
             // Report if call_user_func_array itself had some kind of issue.
             if ($result === false) {
                 $paramsstring = var_export($params, true);
-                throw new \coding_exception(
-                    "webservice override: call_user_func_array returned with false at "
-                    . $externalfunctioninfo->classname
-                    . "::"
-                    . $externalfunctioninfo->methodname
-                    . "("
-                    . $paramsstring
-                    . ");"
-                );
+                $fullname = "{$externalfunctioninfo->classname}::{$externalfunctioninfo->methodname}({$paramsstring})";
+                throw new \coding_exception(get_string('err_sentry_webservfalse', 'local_lbplanner', $fullname));
             }
 
             return $result;
diff --git a/lbplanner/services/courses/get_all_courses.php b/lbplanner/services/courses/get_all_courses.php
index 1d88192a..b17dbecc 100644
--- a/lbplanner/services/courses/get_all_courses.php
+++ b/lbplanner/services/courses/get_all_courses.php
@@ -46,7 +46,7 @@ public static function get_all_courses(): array {
         global $USER;
         $user = user::from_mdlobj($USER);
         if (!($user->get_capabilitybitmask() & (CAPABILITY_FLAG::SLOTMASTER | CAPABILITY_FLAG::TEACHER))) {
-            throw new \moodle_exception('access denied: must be slotmaster');
+            throw new \moodle_exception(get_string('err_accessdenied', 'local_lbplanner'));
         }
 
         $courses = course_helper::get_eduplanner_courses(false);
diff --git a/lbplanner/services/courses/update_course.php b/lbplanner/services/courses/update_course.php
index 06cef154..a5e91f0c 100644
--- a/lbplanner/services/courses/update_course.php
+++ b/lbplanner/services/courses/update_course.php
@@ -69,10 +69,6 @@ public static function update_course(int $courseid, string $color, string $short
             ]
         );
 
-        if (strlen($shortname) > 5) {
-            throw new moodle_exception('Shortname is too long');
-        }
-
         $course = course_helper::get_eduplanner_course($courseid, $USER->id);
 
         if ($color !== null) {
diff --git a/lbplanner/services/notifications/update_notification.php b/lbplanner/services/notifications/update_notification.php
index 44b34501..dba00ea2 100644
--- a/lbplanner/services/notifications/update_notification.php
+++ b/lbplanner/services/notifications/update_notification.php
@@ -65,7 +65,7 @@ public static function update_notification(int $status, int $notificationid) {
         );
 
         if (!$DB->record_exists(notifications_helper::EDUPLANNER_NOTIFICATION_TABLE, ['id' => $notificationid])) {
-            throw new \moodle_exception('Notification does not exist');
+            throw new \moodle_exception(get_string('err_notif_notfound', 'lb_plannerlocal_lbplanner'));
         }
 
         $notification = $DB->get_record(
diff --git a/lbplanner/services/plan/accept_invite.php b/lbplanner/services/plan/accept_invite.php
index 435a1fbf..39a40ab2 100644
--- a/lbplanner/services/plan/accept_invite.php
+++ b/lbplanner/services/plan/accept_invite.php
@@ -61,7 +61,7 @@ public static function accept_invite(int $inviteid) {
         );
 
         if ($invite === false) {
-            throw new \moodle_exception('Invite not found');
+            throw new \moodle_exception(get_string('err_invite_notfound', 'lb_plannerlocal_lbplanner'));
         }
         invite_helper::assert_invite_pending($invite->status);
 
diff --git a/lbplanner/services/plan/clear_plan.php b/lbplanner/services/plan/clear_plan.php
index 342897c5..905db79a 100644
--- a/lbplanner/services/plan/clear_plan.php
+++ b/lbplanner/services/plan/clear_plan.php
@@ -40,7 +40,7 @@ public static function clear_plan_parameters(): external_function_parameters {
      * Clears your current plan.
      *
      * @return void
-     * @throws Exception when access denied
+     * @throws \moodle_exception when access denied
      */
     public static function clear_plan() {
         global $DB, $USER;
@@ -48,7 +48,7 @@ public static function clear_plan() {
         $planid = plan_helper::get_plan_id($USER->id);
 
         if (!plan_helper::check_edit_permissions($planid, $USER->id)) {
-            throw new \Exception('Access denied');
+            throw new \moodle_exception(get_string('err_accessdenied', 'local_lbplanner'));
         }
 
         $DB->delete_records(plan_helper::DEADLINES_TABLE, ['planid' => $planid ]);
diff --git a/lbplanner/services/plan/decline_invite.php b/lbplanner/services/plan/decline_invite.php
index aa7ffd6d..791a777e 100644
--- a/lbplanner/services/plan/decline_invite.php
+++ b/lbplanner/services/plan/decline_invite.php
@@ -59,7 +59,7 @@ public static function decline_invite(int $inviteid) {
         );
 
         if ($invite === false) {
-            throw new \moodle_exception('Invite not found');
+            throw new \moodle_exception(get_string('err_invite_notfound', 'local_lbplanner'));
         }
         invite_helper::assert_invite_pending($invite->status);
 
diff --git a/lbplanner/services/plan/delete_deadline.php b/lbplanner/services/plan/delete_deadline.php
index 6803cadb..8a544174 100644
--- a/lbplanner/services/plan/delete_deadline.php
+++ b/lbplanner/services/plan/delete_deadline.php
@@ -49,7 +49,7 @@ public static function delete_deadline_parameters(): external_function_parameter
      *
      * @param int $moduleid ID of the Module
      * @return void
-     * @throws Exception when access denied
+     * @throws \moodle_exception when access denied
      */
     public static function delete_deadline(int $moduleid) {
         global $DB, $USER;
@@ -64,7 +64,7 @@ public static function delete_deadline(int $moduleid) {
         $planid = plan_helper::get_plan_id($USER->id);
 
         if (!plan_helper::check_edit_permissions($planid, $USER->id)) {
-            throw new \Exception('Access denied');
+            throw new \moodle_exception(get_string('err_accessdenied', 'local_lbplanner'));
         }
 
         $DB->delete_records(
diff --git a/lbplanner/services/plan/invite_user.php b/lbplanner/services/plan/invite_user.php
index 043e0876..2a744658 100644
--- a/lbplanner/services/plan/invite_user.php
+++ b/lbplanner/services/plan/invite_user.php
@@ -64,15 +64,15 @@ public static function invite_user(int $inviteeid): mixed {
         $planid = plan_helper::get_plan_id($USER->id);
 
         if (plan_helper::get_owner($planid) !== intval($USER->id)) {
-            throw new \moodle_exception('Access denied');
+            throw new \moodle_exception(get_string('err_accessdenied', 'local_lbplanner'));
         }
 
-        if ($USER->id === $inviteeid) {
-            throw new \moodle_exception('Cannot invite yourself');
+        if ((int)$USER->id === $inviteeid) {
+            throw new \moodle_exception(get_string('err_invite_yourself', 'local_lbplanner'));
         }
 
         if (plan_helper::get_plan_id($inviteeid) == $planid) {
-            throw new \moodle_exception('Cannot invite user who is already a member');
+            throw new \moodle_exception(get_string('err_invite_alrmember', 'local_lbplanner'));
         }
 
         if (
@@ -81,7 +81,7 @@ public static function invite_user(int $inviteeid): mixed {
                 ['inviteeid' => $inviteeid, 'planid' => $planid, 'status' => PLAN_INVITE_STATE::PENDING]
             )
         ) {
-            throw new \moodle_exception('User is already invited');
+            throw new \moodle_exception(get_string('err_invite_alrinvited', 'local_lbplanner'));
         }
 
         // Save the invite.
diff --git a/lbplanner/services/plan/leave_plan.php b/lbplanner/services/plan/leave_plan.php
index 095762bd..0d583ff8 100644
--- a/lbplanner/services/plan/leave_plan.php
+++ b/lbplanner/services/plan/leave_plan.php
@@ -53,14 +53,15 @@ public static function leave_plan() {
 
         // TODO: remove useless check.
         if (plan_helper::get_access_type($USER->id, $planid) === PLAN_ACCESS_TYPE::NONE) {
-            throw new \moodle_exception('User is not a member of this plan');
+            throw new \moodle_exception(get_string('err_plan_cantremove_userfromother', 'local_lbplanner'));
         }
 
+        // TODO: factor this out into plan_helper.
         if (plan_helper::get_access_type($USER->id, $planid) === PLAN_ACCESS_TYPE::OWNER) {
             $members = plan_helper::get_plan_members($planid);
 
             if (count($members) == 1) {
-                throw new \moodle_exception('Cannot Leave Plan: Plan must have at least one other member');
+                throw new \moodle_exception(get_string('err_plan_cantleave_empty', 'local_lbplanner'));
             }
 
             $writemembers = [];
diff --git a/lbplanner/services/plan/set_deadline.php b/lbplanner/services/plan/set_deadline.php
index b6639e9e..f149726b 100644
--- a/lbplanner/services/plan/set_deadline.php
+++ b/lbplanner/services/plan/set_deadline.php
@@ -82,7 +82,7 @@ public static function set_deadline(int $moduleid, int $deadlinestart, int $dead
         $planid = plan_helper::get_plan_id($USER->id);
 
         if (!plan_helper::check_edit_permissions($planid, $USER->id)) {
-            throw new \moodle_exception('Access denied');
+            throw new \moodle_exception(get_string('err_accessdenied', 'local_lbplanner'));
         }
 
         $deadline = $DB->get_record(plan_helper::DEADLINES_TABLE, ['moduleid' => $moduleid, 'planid' => $planid]);
diff --git a/lbplanner/services/plan/update_access.php b/lbplanner/services/plan/update_access.php
index 5219a1a1..c6e14061 100644
--- a/lbplanner/services/plan/update_access.php
+++ b/lbplanner/services/plan/update_access.php
@@ -72,25 +72,27 @@ public static function update_access(int $accesstype, int $memberid) {
         $planid = plan_helper::get_plan_id($USER->id);
 
         if (plan_helper::get_owner($planid) !== intval($USER->id)) {
-            throw new \moodle_exception('Access denied');
+            throw new \moodle_exception(get_string('err_accessdenied', 'local_lbplanner'));
         }
 
+        // TODO: factor out into plan_helper.
+
         $accesstypeobj = PLAN_ACCESS_TYPE::try_from($accesstype);
 
         if ($accesstypeobj === null) {
-            throw new \moodle_exception('Access type not valid');
+            throw new \moodle_exception(get_string('err_plan_changeaccess_inval', 'local_lbplanner'));
         }
 
         if ($USER->id === $memberid) {
-            throw new \moodle_exception('Cannot change own permissions');
+            throw new \moodle_exception(get_string('err_plan_changeaccess_self', 'local_lbplanner'));
         }
 
         if (plan_helper::get_owner($planid) == $memberid) {
-            throw new \moodle_exception('Cannot change permissions for the plan owner');
+            throw new \moodle_exception(get_string('err_plan_changeaccess_ofowner', 'local_lbplanner'));
         }
 
         if ($accesstypeobj === PLAN_ACCESS_TYPE::OWNER) {
-            throw new \moodle_exception('Cannot change permission to owner');
+            throw new \moodle_exception(get_string('err_plan_changeaccess_toowner', 'local_lbplanner'));
         }
 
         $access = $DB->get_record(plan_helper::ACCESS_TABLE, ['planid' => $planid, 'userid' => $memberid], '*', MUST_EXIST);
diff --git a/lbplanner/services/plan/update_plan.php b/lbplanner/services/plan/update_plan.php
index 1b2e00b5..4fa05ffd 100644
--- a/lbplanner/services/plan/update_plan.php
+++ b/lbplanner/services/plan/update_plan.php
@@ -49,7 +49,7 @@ public static function update_plan_parameters(): external_function_parameters {
      *
      * @param string $planname Name of the Plan
      * @return void
-     * @throws Exception when access denied
+     * @throws \moodle_exception when access denied
      */
     public static function update_plan(string $planname) {
         global $DB, $USER;
@@ -62,7 +62,7 @@ public static function update_plan(string $planname) {
         $planid = plan_helper::get_plan_id($USER->id);
 
         if (!plan_helper::check_edit_permissions($planid, $USER->id)) {
-            throw new \Exception('Access denied');
+            throw new \moodle_exception(get_string('err_accessdenied', 'local_lbplanner'));
         }
 
         $plan = $DB->get_record(plan_helper::TABLE, ['id' => $planid], '*', MUST_EXIST);
diff --git a/lbplanner/services/slots/add_slot_filter.php b/lbplanner/services/slots/add_slot_filter.php
index cad122b7..c2074933 100644
--- a/lbplanner/services/slots/add_slot_filter.php
+++ b/lbplanner/services/slots/add_slot_filter.php
@@ -81,10 +81,6 @@ public static function add_slot_filter(int $slotid, ?int $courseid, ?string $vin
 
         // Check if user is supervisor for this slot, throw error if not.
         slot_helper::assert_slot_supervisor($USER->id, $slotid);
-        // Ensure that either $courseid or $vintage are non-null.
-        if (is_null($courseid) && is_null($vintage)) {
-            throw new \moodle_exception('courseid and vintage can\'t both be null');
-        }
 
         $filter = new slot_filter(0, $slotid, $courseid, $vintage);
 
diff --git a/lbplanner/services/slots/book_reservation.php b/lbplanner/services/slots/book_reservation.php
index e31837a5..2e49839c 100644
--- a/lbplanner/services/slots/book_reservation.php
+++ b/lbplanner/services/slots/book_reservation.php
@@ -88,12 +88,12 @@ public static function book_reservation(int $slotid, string $date, int $userid):
         $now = new DateTimeImmutable('today', $utctz);
         $dateobj = DateTimeImmutable::createFromFormat("Y-m-d", $date, $utctz);
         if ($dateobj === false) {
-            throw new \moodle_exception("invalid date formatting: got '{$date}', must be YYYY-MM-DD");
+            throw new \moodle_exception(get_string('err_dateformat', 'local_lbplanner', $date));
         }
         $td = $now->diff($dateobj);
 
         if ($td->invert === 1) {
-            throw new \moodle_exception('Can\'t reserve date in the past');
+            throw new \moodle_exception(get_string('err_reserv_past', 'local_lbplanner'));
         }
 
         $maxdays = null;
@@ -115,26 +115,26 @@ public static function book_reservation(int $slotid, string $date, int $userid):
         }
 
         if ($td->days > $maxdays) {
-            throw new \moodle_exception("Date is past allowed date ({$maxdays} days in the future)");
+            throw new \moodle_exception(get_string('err_reserv_toofuture', 'local_lbplanner', $maxdays));
         }
 
         $slot = slot_helper::get_slot($slotid);
 
         // Check if user has access to slot.
         if (count(slot_helper::filter_slots_for_user([$slot], $student)) === 0) {
-            throw new \moodle_exception('Student does not have access to this slot');
+            throw new \moodle_exception(get_string('err_reserv_studentnoaccess', 'local_lbplanner'));
         }
 
         // Check if user is already in slot.
         foreach (slot_helper::get_reservations_for_slot($slotid) as $tmpreservation) {
             if ($tmpreservation->userid === $userid) {
-                throw new \moodle_exception('Student is already in slot');
+                throw new \moodle_exception(get_string('err_reserv_studentalrin', 'local_lbplanner'));
             }
         }
 
         // Check if slot is full.
         if ($slot->get_fullness() >= $slot->size) {
-            throw new \moodle_exception('Slot is already full');
+            throw new \moodle_exception(get_string('err_reserv_slotfull', 'local_lbplanner'));
         }
 
         $reservation = new reservation(0, $slotid, $dateobj, $userid, $curuserid);
diff --git a/lbplanner/services/slots/delete_slot_filter.php b/lbplanner/services/slots/delete_slot_filter.php
index bab51257..6b6baa48 100644
--- a/lbplanner/services/slots/delete_slot_filter.php
+++ b/lbplanner/services/slots/delete_slot_filter.php
@@ -64,7 +64,7 @@ public static function delete_slot_filter(int $filterid): void {
 
         // Check if user is supervisor for this slot, throw error if not.
         if (!slot_helper::check_slot_supervisor($USER->id, $filter->slotid)) {
-            throw new \moodle_exception('Insufficient Permission: you\'re not supervisor of this filter\'s associated slot');
+            throw new \moodle_exception(get_string('err_accessdenied', 'local_lbplanner'));
         }
 
         // Delete filter.
diff --git a/lbplanner/services/slots/get_all_slots.php b/lbplanner/services/slots/get_all_slots.php
index f612370c..23f477a8 100644
--- a/lbplanner/services/slots/get_all_slots.php
+++ b/lbplanner/services/slots/get_all_slots.php
@@ -47,7 +47,7 @@ public static function get_all_slots(): array {
         $user = user::from_mdlobj($USER);
 
         if (!($user->get_capabilitybitmask() & CAPABILITY_FLAG::SLOTMASTER)) {
-            throw new \moodle_exception('current user is not slotmaster');
+            throw new \moodle_exception(get_string('err_accessdenied', 'local_lbplanner'));
         }
         $slots = slot_helper::get_all_slots();
 
diff --git a/lbplanner/services/slots/unbook_reservation.php b/lbplanner/services/slots/unbook_reservation.php
index 3fe80f11..d984797b 100644
--- a/lbplanner/services/slots/unbook_reservation.php
+++ b/lbplanner/services/slots/unbook_reservation.php
@@ -77,25 +77,24 @@ public static function unbook_reservation(int $reservationid, bool $nice): void
         $startpast = $endpast || ($now->diff($reservation->get_datetime())->invert === 1);
 
         if ($userid === $reservation->userid) {
-            if ($startpast) {
-                throw new \moodle_exception('You can\'t unbook this reservation because it has already started');
+            if ($endpast) {
+                throw new \moodle_exception(get_string('err_reserv_unreserv_alrended', 'local_lbplanner'));
+            } else if ($startpast) {
+                throw new \moodle_exception(get_string('err_reserv_unreserv_alrstarted', 'local_lbplanner'));
             }
         } else if (slot_helper::check_slot_supervisor($userid, $reservation->slotid)) {
             if ($endpast) {
-                throw new \moodle_exception('You can\'t unbook this reservation because it has already ended');
+                throw new \moodle_exception(get_string('err_reserv_unreserv_alrended', 'local_lbplanner'));
             }
             if ($nice) {
                 if ($startpast) {
-                    throw new \moodle_exception(
-                        'Students can\'t unbook reservations that have already started.'
-                        . ' If you want to unbook this reservation regardless, force it.'
-                    );
+                    throw new \moodle_exception(get_string('err_reserv_unreserv_alrstartedorforce', 'local_lbplanner'));
                 }
                 notifications_helper::notify_user($reservation->userid, $reservation->id, NOTIF_TRIGGER::UNBOOK_REQUESTED);
                 return;
             }
         } else {
-            throw new \moodle_exception('insufficient permission to unbook this reservation');
+            throw new \moodle_exception(get_string('err_accessdenied', 'local_lbplanner'));
         }
 
         $DB->delete_records(
diff --git a/lbplanner/services/slots/update_slot.php b/lbplanner/services/slots/update_slot.php
index 2b7a6761..716f4ef0 100644
--- a/lbplanner/services/slots/update_slot.php
+++ b/lbplanner/services/slots/update_slot.php
@@ -125,7 +125,7 @@ public static function update_slot(int $id, ?int $startunit, ?int $duration, ?in
         );
         // Check if slot is now overfull, and notify frontend via exception if so.
         if ($slot->get_fullness() > $slot->size) {
-            throw new \moodle_exception('Slot is now overfull!');
+            throw new \moodle_exception(get_string('err_slot_overfull', 'local_lbplanner'));
         }
     }
 
diff --git a/lbplanner/services/user/delete_user.php b/lbplanner/services/user/delete_user.php
index 8a60580c..8e7e042c 100644
--- a/lbplanner/services/user/delete_user.php
+++ b/lbplanner/services/user/delete_user.php
@@ -50,7 +50,7 @@ public static function delete_user() {
 
         // Check if User is in user table.
         if (!$DB->record_exists(user_helper::EDUPLANNER_USER_TABLE, ['userid' => $userid])) {
-            throw new moodle_exception('User is not registered in Eduplanner');
+            throw new moodle_exception(get_string('err_user_notfound', 'local_lbplanner'));
         }
 
         $planid = plan_helper::get_plan_id($userid);
@@ -61,6 +61,7 @@ public static function delete_user() {
             &&
             !(plan_helper::get_access_type($planid, $userid) == PLAN_ACCESS_TYPE::OWNER)
         ) {
+            // TODO: replace with plan_helper function.
             self::call_external_function('local_lbplanner_plan_leave_plan', ['userid' => $userid, 'planid' => $planid]);
         }
         $DB->delete_records(plan_helper::DEADLINES_TABLE, ['planid' => $planid]);
@@ -83,6 +84,7 @@ public static function delete_user() {
 
         // Deleting all Courses associated with the User.
         $DB->delete_records(course_helper::EDUPLANNER_COURSE_TABLE, ['userid' => $userid]);
+        // TODO: delete kanban, slot, slot_filter & reservation data
         // Deleting User from User table.
         $DB->delete_records(user_helper::EDUPLANNER_USER_TABLE, ['userid' => $userid]);
     }
diff --git a/lbplanner/settings.php b/lbplanner/settings.php
index e36e054a..fead9c72 100644
--- a/lbplanner/settings.php
+++ b/lbplanner/settings.php
@@ -30,28 +30,31 @@
     $settings = new admin_settingpage('local_lbplanner', 'EduPlanner');
     $ADMIN->add('localplugins', $settings);
 
+    $daysingular = get_string('unit_day', 'local_lbplanner');
+    $dayplural = get_string('unit_day_pl', 'local_lbplanner');
+
     $futuresightsett = new admin_setting_configselect(
         'local_lbplanner/' . SETTINGS::SLOT_FUTURESIGHT,
-        'Advance reservation limit',
-        'Maximum number of days in advance students can reserve slots (0 = same day only).',
+        get_string('sett_futuresight_title', 'local_lbplanner'),
+        get_string('sett_futuresight_desc', 'local_lbplanner'),
         3,
         [
-            0 => "0 Days",
-            1 => "1 Day",
-            2 => "2 Days",
-            3 => "3 Days",
-            4 => "4 Days",
-            5 => "5 Days",
-            6 => "6 Days",
-            7 => "7 Days",
+            0 => "0 {$dayplural}",
+            1 => "1 {$daysingular}",
+            2 => "2 {$dayplural}",
+            3 => "3 {$dayplural}",
+            4 => "4 {$dayplural}",
+            5 => "5 {$dayplural}",
+            6 => "6 {$dayplural}",
+            7 => "7 {$dayplural}",
         ],
     );
     $settings->add($futuresightsett);
 
     $outdaterangesett = new admin_setting_configduration(
         'local_lbplanner/' . SETTINGS::COURSE_OUTDATERANGE,
-        'Mark courses as outdated after',
-        'The maximum duration a course remains visible in EduPlanner after it ends.',
+        get_string('sett_outdaterange_title', 'local_lbplanner'),
+        get_string('sett_outdaterange_desc', 'local_lbplanner'),
         31536000, // 1 non-leap year.
         86400, // In days.
     );
@@ -60,8 +63,8 @@
 
     $sentrydsnsett = new admin_setting_configtext(
         'local_lbplanner/' . SETTINGS::SENTRY_DSN,
-        'Sentry DSN',
-        'for where to send error debugging info to.',
+        get_string('sett_sentrydsn_title', 'local_lbplanner'),
+        get_string('sett_sentrydsn_desc', 'local_lbplanner'),
         '',
         PARAM_TEXT
     );
@@ -69,8 +72,8 @@
 
     $panicsett = new admin_setting_configcheckbox(
         'local_lbplanner/' . SETTINGS::PANIC,
-        'PANIC SWITCH',
-        'Turns API off - only use in emergencies. No data loss, but total loss of EduPlanner services until box is unchecked.',
+        get_string('sett_panic_title', 'local_lbplanner'),
+        get_string('sett_panic_desc', 'local_lbplanner'),
         '0',
     );
     $settings->add($panicsett);