diff --git a/src/frame/middleware/index.ts b/src/frame/middleware/index.ts
index 46d5c3263c0a..cc470946f46d 100644
--- a/src/frame/middleware/index.ts
+++ b/src/frame/middleware/index.ts
@@ -21,7 +21,7 @@ import detectLanguage from '@/languages/middleware/detect-language'
 import reloadTree from './reload-tree'
 import context from './context/context'
 import shortVersions from '@/versions/middleware/short-versions.js'
-import languageCodeRedirects from '@/redirects/middleware/language-code-redirects.js'
+import languageCodeRedirects from '@/redirects/middleware/language-code-redirects'
 import handleRedirects from '@/redirects/middleware/handle-redirects'
 import findPage from './find-page.js'
 import blockRobots from './block-robots.js'
diff --git a/src/languages/lib/languages.d.ts b/src/languages/lib/languages.d.ts
new file mode 100644
index 000000000000..6129a4ac88b2
--- /dev/null
+++ b/src/languages/lib/languages.d.ts
@@ -0,0 +1,23 @@
+type Language = {
+  name: string
+  nativeName?: string
+  code: string
+  hreflang: string
+  redirectPatterns?: RegExp[]
+  dir: string
+}
+type Languages = {
+  [code: string]: Language
+}
+
+export const allLanguageKeys: string[]
+
+export const languageKeys: string[]
+
+export const languagePrefixPathRegex: RegExp
+
+export declare function pathLanguagePrefixed(path: string): boolean
+
+const languages: Languages
+
+export default languages
diff --git a/src/redirects/middleware/language-code-redirects.js b/src/redirects/middleware/language-code-redirects.ts
similarity index 62%
rename from src/redirects/middleware/language-code-redirects.js
rename to src/redirects/middleware/language-code-redirects.ts
index d1150b2669d7..1b64ef769855 100644
--- a/src/redirects/middleware/language-code-redirects.js
+++ b/src/redirects/middleware/language-code-redirects.ts
@@ -1,5 +1,8 @@
-import languages from '#src/languages/lib/languages.js'
-import { defaultCacheControl } from '#src/frame/middleware/cache-control.js'
+import type { NextFunction, Response } from 'express'
+
+import languages from '@/languages/lib/languages.js'
+import { defaultCacheControl } from '@/frame/middleware/cache-control.js'
+import { ExtendedRequest } from '@/types'
 
 const redirectPatterns = Object.values(languages)
   .map((language) => language.redirectPatterns || [])
@@ -16,14 +19,18 @@ const allRedirectPatterns = Object.values(languages)
   .map((language) =>
     (language.redirectPatterns || []).map((redirectPattern) => [language.code, redirectPattern]),
   )
-  .flat()
+  .flat() as [string, RegExp][] // Seems TypeScript didn't understand the .flat()
 
 // This middleware handles redirects for mistyped language codes
 //
 // Examples:
 // /jp*    -> /ja*
 // /zh-TW* -> /zh*
-export default function languageCodeRedirects(req, res, next) {
+export default function languageCodeRedirects(
+  req: ExtendedRequest,
+  res: Response,
+  next: NextFunction,
+) {
   // Only in the unlikely event that the `req.path` starts with one of these
   // prefixes do we bother looking up what the redirect should be.
   if (req.path.startsWith('/_next/static')) return next()
@@ -32,10 +39,13 @@ export default function languageCodeRedirects(req, res, next) {
 
   // This loop is almost never ever used so it doesn't have to be
   // particularly smart or fast.
-  const [code, pattern] = allRedirectPatterns.find(([, pattern]) => pattern.test(req.path))
-  if (code && pattern) {
-    defaultCacheControl(res)
-    return res.redirect(301, req.path.replace(pattern, `/${code}`))
+  const matched = allRedirectPatterns.find(([, pattern]) => pattern.test(req.path))
+  if (matched) {
+    const [code, pattern] = matched
+    if (code && pattern) {
+      defaultCacheControl(res)
+      return res.redirect(301, req.path.replace(pattern, `/${code}`))
+    }
   }
   return next()
 }