Revamp internationalization section

- Adapt the contents of the tips for i18n page into the main
internationalization one.
- Change reference from tipsfortranslators to the internationalization page in
the about->supported languages page.

Testing Done:
Ran `dev-server.sh` and verified content looks as intended.

Bugs closed: NEST-33

Reviewed at https://reviews.imfreedom.org/r/807/