Even for people with a Romanic language background, English is the de-facto new lingua franca. 
That’s the point. I think it’s parsimonious to try sticking to English, and not split the forum in multiple sub-thingies. There are less than 60 k FP users from all over Europe (with some rare exceptions on other contients). The majority of customers comes from countries with languages which are somehow related to English. And while Google Translate is not yet as good as the original Babel fish, it can give you both an idea and help to translate to English from you native tongue, even if it’s not related to English.
However, of course everybody can ask questions in any language of choice. People providing help can (additionaly) provide it in his or her native tongue, if possible. I wouldn’t be the really surprised if a question asked in Chinese or even Bambara would get an answer here. However, it is easier to get answers if a question is asked in English.
Your second thought seems sensible, though: it would be easy for everyone to add a [language] in brackets to a new topic, so anyone could search for stuff written in Francais, Deutsch, Catala, Hindi or whatever you want to answer today. Or skip it, if you don’t want to try to make sense of, e.g., eye-soaring German grammar. 