The main language of the forum is English. But I can imagine that not every potential user is fluent/comfortable enough to ask a question in English. I would suggest that a question can be asked in any language and then the moderators will make sure that someone speaking this language can translate the problem into English. The solution should again be posted in English and be translated back to the language in which the question was asked.
Enabling language moderation could either be done via tagging, which requires the moderators to know who speaks what. Or language tags get introduced, which will make it more self-driving. Since every user can filter according to tags.
And while I am writing this the first post is made about this topic: Translation between Spanish and English of COVID-19 problems and replies