To give another deviant a direct link to this FAQ answer, use the following code in your comment or forum post:
Are we allowed to post forum threads in languages other than English?
In order to provide fair moderation in the Main and Gallery Forums, we ask that you post in English. Any threads which are not posted in English will be closed.
If you are a subscriber, you can post in other languages in your own forums, which are linked from your journal page.