[Feat] Add full multilingual (i18n) support across user-facing messages

[SanidhyaMadheshia]

What do we need?

The app currently lacks full multilingual support. While Rocket.Chat i18n is used
for settings labels, most user-facing strings (messages, modals, commands, and
notifications) are hardcoded in English.

We need a centralized internationalization (i18n) system so that all user-facing
text can be translated and displayed based on the user's preferred language or
Rocket.Chat locale.

This solves the issue where non-English users receive English-only responses
even when Rocket.Chat is configured for another language.

Without full i18n support:

• The app is not accessible to global users
• Language consistency is broken
• Adding new languages in the future is difficult

Proper multilingual support makes the app production-ready and usable by
international teams.

Acceptance Criteria

• Create a centralized translation configuration (i18n module)
• Replace hardcoded English strings with translation keys
• Update mainAppResponses to return localized strings
• Localize all modals (titles, buttons, body text)
• Localize slash command descriptions and help messages
• Store and retrieve user language preference
• Fallback to English when translation is missing
• Ensure no user-facing runtime text is hardcoded

Relevant ScreenShots

N/A – issue identified via code inspection.

Affected files include:

• mainAppResponses.ts
• Command handlers
• Modal components (GetLocationModal, ReminderModal)
• Slash command definitions

Further Comments

This feature can leverage Rocket.Chat’s existing i18n infrastructure while adding
app-level translation management.

Optional future enhancement:

• Auto-detect language from Rocket.Chat locale
• Add a slash command to manually set preferred language

[SanidhyaMadheshia]

@thepiyush-303 can you please assign me this issue ? I would like to work on this

[thepiyush-303]

Sure @SanidhyaMadheshia You can work on the issue no need of assignment,

• I would suggest you to add a select option to change languages in the app's setting instead of creating a new slash-command.
• Also no need of creating too many languages, adding following languages would be enough
  German, English, Polish, Portuguese, Russian.