Add i18n

[LucaBernstein]

• As comands are valid for each user, there are multiple ways on how to implement this
  • Bind commands in multiple languages simultaneously
  • Only use .OnText binding, check user language (cached?), lookup command and execute. Might require a custom command handler, we might even be able to reuse the subcommands handler.

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• [ ] Check for possible library to use, e.g. https://github.com/nicksnyder/go-i18n
• [ ] translation files in an i18n/translations directory
• [ ] Translate existing project (extract EN)
• [ ] Check that everything works for one langauge
• [ ] Add another language (DE)
• [ ] Make configurable in /config
  • e.g. /config lang [de|en|...]
• [ ] implement PoC regarding handling translated commands for both possibilities suggested above
  • [ ] decide for one possibility
• [ ] implement decided solution, write tests

[LucaBernstein]

Also translate commands?