Improve localization support for 3rd parties

There are more languages in the world than the officially supported English, Swedish and Finnish. The REMS team can't maintain all the translations in the world. We should however distribute all translations in our releases. A developer working with another language could help us.

We can improve this collaboration by:
- [ ] Splitting languages into official and community languages.
- [ ] Building should break if official languages are missing something (as per today it does).
- [ ] Building a tool to report missing or changed translations wrt. community languages.
- [ ] If a community language is used, but it has problems in the report (after including extra translations), prevent that REMS instance from starting and produce a clear error message.

If the new build-time reporting tool saves to a file at build time the hash of each translation text or the Git commit hash, then we can report which translation keys are new or changed compared to the hash of a community translation. Then our collaborators can easily check if they really need to change or not.

No files, tests, or entry points are named. Start by locating the translation definitions, release packaging, and current build validation for English, Swedish, and Finnish. Clarify the official/community language workflow, reporting behavior, and startup failure requirements, then verify that releases include community translations and expose the requested diagnostics.

Written by the indexing model from the issue text.