Implement i18n

[diamondburned]

This issue tracks progress for implementing internationalization in gtkcord4.

• [ ] i18n support in gotkit
  • [x] Base support for .po files
  • [x] Domain support
  • [ ] Full translations for "gotkit" domain
  • [ ] Optional: Merge .po files into "default" domain
• [ ] i18n support in gtkcord4
  • [ ] Wrap all gtkcord4 strings around locale.Get
  • [x] Example translations for a language
• [ ] Optional: static analyzing tool for extracting string literals

[diamondburned]

For example .po file, see https://github.com/diamondburned/gtkcord4/blob/main/po/vi/default.po.

[diamondburned]

To test, run with LC_ALL, e.g. LC_ALL=vi go run .. Rebuilding is required for now.