Since we keep getting off topic over in the fanfic pet peeves thread, I thought we might just make a second one.
If you have questions about grammar, spelling, punctuation, or anything else regarding language, feel free to ask in here. Instead of just nit-picking fanfic, we can help people with it.
Here are some links to sister threads that you may also find useful:
Fanfic Pet Peeves
Fanfic Helpdesk: Technical and Scientific Help for Writers
Plot Bunny Adoption
For other languages, I suggest an off-site forum, as there are many languages used there and you can get plenty of help with the details of the grammar, etc.
Language Learning Forum