Add Spanish (and other languages) UI localization support

Feature Request: UI localization / Spanish interface support

Currently, the \language\ setting in \settings.json\ only changes the language of Claude's responses, but the Claude Code interface (input placeholder 'Ask a question...', buttons, menus, etc.) remains in English with no way to change it.

It would be very useful to have full UI localization support, especially for Spanish-speaking users in Latin America and Spain who represent a large portion of the user base.

Current behavior: Interface is English-only regardless of system language or \language\ setting.

Expected behavior: UI elements should respect the user's preferred language, similar to how VS Code handles language packs.