I say go ahead and write in whatever language you want, just don't expect many to reply if it's not in American English because that is the language of the U.S. and this is the "U.S. Message Board".....
Yes, sure, but English is the international language (and I think that writing in the British or Canadian one will be OK too

) which enables all nations to communicate to each other. Imagine that groups of Italians, Russians, Chinese etc. discuss something in their native languages in every thread. Sure, you can put them on the ignore list, but what sense does such practice make? It's an English-speaking forum and indeeed it's the 'US Message Board'. So I think that if foreigners come here it's much better if they speak English. Occasional Russian (or any other language) is OK when it's a quotation, for example, but I think that all discussions should be in English.