I know in locals there are some people who aren't comfortable posting with their languages so they uses the one which they finds it interesting to post with, your main interest should be focused on whether the post is readable or not, meaningful and conveying the required information if not on topics then such post should be reported to the mod for immediate deletion.
Why should one be uncomfortable to post in their own language in local board? This just seems illogical.
Just take for instance of our LB since we doesn't have any particular language to speak we prefer pidgin why because we have about 3 ethnic groups with over 300 languages. Now come to think of where everyone write a post with their language how do we understand others, the official language is pidgin in english were we understand each others. But I know this may not be applicable to others that only speaks one general language, in some cases if it's a must do rules then speaking english is not allowed and they should only focused on the acceptable language than english.