I don't think that it is worth spending time and resources on this. The overall volume on the forum right now is so low that it will be even lower in separate language forums and it will reduce the exposure to people able to answer for example questions to specific issues...
I don't know what mix of native languages among the regulars here is, but I think that everyone should be able to try and post in English, given that people provide more than half a sentence of information.
And if someone indeed is not sure about his/her language skills, mentioning what his/her native language is might help that someone versed in both that language and English can help out...
Ralf