UI language change not applied (affects multiple languages) on macOS

What version of the Codex App are you using (From “About Codex” dialog)?

Version 26.325.31654 (1272)

What subscription do you have?

Personal account (Plus)

What platform is your computer?

Darwin 25.1.0 arm64 arm

What issue are you seeing?

Changing the UI language in the Codex macOS app does not take effect.

This issue is not limited to Vietnamese. Other available languages also do not apply after selection.

The language option is visible in Settings, but selecting a different language has no effect on the UI.

<img width="1470" height="1518" alt="Image" src="https://github.com/user-attachments/assets/ffdb8fb9-e494-4abb-a343-e5199024de5a" />

What steps can reproduce the bug?

1. Open Codex app
2. Open Settings (via Command Palette or macOS menu bar)
3. Navigate to Language section
4. Select a different language (e.g. Vietnamese or other non-English options)
5. Restart the app (Cmd + Q → reopen)

The UI remains in English.

What is the expected behavior?

The UI should switch to the selected language after restarting the app.

Additional information

• Issue reproducible 100%
• Not limited to Vietnamese — affects multiple languages
• No error message or feedback is shown
• App logs show successful config/read and experimentalFeature calls

Possibly related to #16224