Language switch on welcome screen not working — text remains in English

[Smolcup]

Describe the bug
When changing the language on the welcome screen (before logging in), the UI does not update. The heading "Welcome to Checkmate" and all login page text remain in English regardless of which language is selected.

To Reproduce
Steps to reproduce the behavior:

1. Open Checkmate in the browser (combined version)
2. Click on the language selector
3. Select any non-English language
4. The page text does not change, still showing "Welcome to Checkmate" and the credential problems still described in English (forgot password?...)

Expected behavior
The welcome message, login form labels,button text, the logging in messages (Forgot password, Don't have an account?) as well as their buttons should update to the selected language immediately.

Screenshots

Desktop (please complete the following information):

• Browser Opera GX
• Version 3.1.7

Additional context
Refreshing the page does not do anything.

[mayssagl]

I was able to reproduce this bug on the demo server.
Steps followed:

1. Opened the welcome screen
2. Changed language to French
3. Text remained in English

Browser: Chrome
OS: Windows
Version: 3.1.7

[Smolcup]

I've investigated this issue and found the root cause. A fix has been submitted in this Pull Request: #3450
Root cause: LanguageSelector.tsx was only saving the language selection to Redux state via setLanguage(), but never calling i18n.changeLanguage() to actually tell the i18next library to switch the UI language. Additionally, several locale files were missing the pages.auth translation keys, causing raw key names to display instead of translated text.