More languages, and flags in the language picker

Two parts:

1. Expand translated spaces beyond the current set — decide the target language list first; the translation pipeline is the real cost.
2. Make the language picker friendlier, e.g. show flag icons next to the language names.

Start by defining the target language list, then review the existing translation pipeline and language picker entry point. Clarify the scope of flag icons and translation workflow before implementation. Done means the agreed languages are supported and the picker presents them with the approved visual treatment.

Written by the indexing model from the issue text.