Feature Request: Add internationalization (i18n) support for multi-language users

[hoteye]

What feature would you like to see?

Background

Codex CLI currently only supports English text throughout the user interface, error messages, and documentation. While there is basic locale-aware number formatting using ICU libraries, there's no comprehensive internationalization system for text content.

Current State Analysis

After analyzing the Codex CLI codebase, I found:

Existing locale support:

• Basic number formatting with ICU libraries (icu_decimal, icu_locale_core, sys-locale) in codex-rs/protocol/src/num_format.rs

Missing i18n infrastructure:

• ~926 hardcoded English strings across the codebase
• No translation framework or resource files
• No string extraction/management system
• User-facing text in CLI, TUI, and error messages all in English only

Proposed Enhancement

Implement comprehensive internationalization to make Codex CLI accessible to non-English speaking developers worldwide.

Benefits

• Global accessibility: Enable developers from different language backgrounds to use Codex effectively
• Market expansion: Broader adoption in international developer communities
• Better user experience: Improved usability for global teams and organizations
• Issue resolution: Would address existing character encoding problems like Turkish character issue #3077 (Turkish character support)

Target Languages (Initial)

• English (en-US) - baseline
• Chinese Simplified (zh-CN) - large developer community
• Spanish (es-ES) - growing market
• Japanese (ja-JP) - active developer base

Are you interested in implementing this feature?

Yes, I'm ready to contribute this feature implementation. I have proven experience with CLI internationalization:

My relevant contributions:

• Google Gemini CLI #7774 - Initial i18n implementation
• Google Gemini CLI #8060 - Extended i18n support
• Ink Framework #766 - Proposed i18n solution for React CLI components

What I can deliver:

• Complete technical design document with framework selection rationale
• Migration plan for existing hardcoded strings
• Full implementation of i18n infrastructure
• Initial translations for core languages
• Developer documentation for future translators
• Automated tooling for translation management

My expertise:

• Deep understanding of Rust i18n patterns
• Experience with translation workflows and community management
• Full-cycle development from infrastructure to deployment

Please wait for acknowledgement before implementing or opening a PR.

Additional information

Technical Implementation Plan

Based on successful patterns from my Gemini CLI work:

Phase 1: Core Infrastructure

• Integrate fluent-rs or similar Rust i18n framework
• Create locale file structure (locales/en-US.ftl, locales/zh-CN.ftl, etc.)
• Implement string extraction tooling
• Add fallback mechanism (English as default)

Phase 2: Critical Strings

• Error messages and warnings
• Core CLI commands help text
• User prompts and confirmations
• Configuration validation messages

Phase 3: Extended Coverage

• TUI interface text
• Advanced help documentation
• Configuration descriptions
• Debug and logging messages

Related Issues

This proposal would also address existing character encoding issues like #3077 (Turkish character support) by implementing comprehensive Unicode and multi-language support.

Community Impact

This enhancement aligns with modern CLI tool standards and would significantly improve Codex's accessibility for the global developer community, potentially increasing adoption in international markets.

I'm available to discuss technical approach, timeline, and any specific requirements for Codex CLI's internationalization strategy.

[hoteye]

Hi @bolinfest,
This issue has been open for quite a while with no response.
As I'm ready to contribute and have experience with CLI internationalization, could you please take a look or share your thoughts on the proposed i18n support?
Your feedback or guidance would be greatly appreciated. Thanks!

[ahasasjeb]

我觉得得等这个项目迭代慢下来再说i18n吧

[nos1609]

Can help with UI/cli translation to:

• Russian
• French
• Italian

[hoteye]

@jif-oai , is i18n support something the team would consider? Would appreciate any guidance before I invest time in implementation.

[etraut-openai]

@hoteye, thanks for the offer, but this is a feature that the codex team will need to implement. It will need to be designed in a way that allows us to maintain it over time as strings are removed, updated, and added.

[onevcat]

Additional use case: in the Codex CLI TUI, the gray reasoning/log panel is always English. For non‑English users, it’s hard to read.

Request: add i18n/locale override for all TUI text including reasoning events, or at least a config key (e.g. ui_locale/output_locale) so reasoning/logs follow the assistant’s language. This should cover the gray reasoning area shown during CLI sessions, not just prompts and errors.