Update about the current translation state:
The following languages have been started, but are inactive with insufficient content: Greek, Esperanto, Hungarian and Romanian. No work has recently been done. Unless some really dedicated translator starts working on these I see no chance to make them officially supported.
Finnish looks better but also needs a bit more coverage to be put in the menu. Only a very small number of Raven/Strife texts have been done so far.
The following languages are active in the menu but still missing content:
Italian: Missing Hexen text screens, most of Strife's dialogues, and none of Chex Quest, Hacx and Harmony was translated. For the last 3 games I tried to fill in as much as possible with Google Translate but I won't give any guarantees about correctness and quality of translation here, it was just to ensure that the immediately visible parts do not show up in English. Altogether there's roughly 1250 texts still missing, the majority coming from Strife.
Polish: Strife is roughly half done, Hacx and Harmony hasn't started yet. Altogether there's roughly 920 texts missing, again with the majority coming from Strife.
Russian and Czech: Hacx and Harmony are still untranslated, but with active translators being present I think these will be done eventually.
German, French, Korean, Spanish and Portuguese are complete as of now, although some text may yet have to be reviewed for European Portuguese.
Right now the most urgent stuff to fill in is the Chex Quest, Hacx and Harmony texts for Italian and Polish, if someone can help here it'd be very much appreciated.