Hi @flyheli,
According to the Code of Conduct, you must use English when posting on the forums. The one exception is the #multiplayer category, where you can use any language to help you find users to connect with.
If you cannot read English, the forums provide a handy feature that translates posts into your native language, you can use this feature by clicking the translate button under a post. 
If you need help converting a post from your language to English, try using Bing Translator, the same service used by the forums.