There are a quite a few language learning related sites on the Stack Exchange network. I may have missed a few, but here they are:
It would be nice to have a single language related site and use tags when asking questions about a specific language. Stack Overflow already does something similar for programming languages.
- Automatic support for minority or endangered languages. There are thousands of languages that will never have enough support to create their own SE site. Yet many have a core group of learners and researchers that would benefit from being able to ask and answer questions just by adding a new tag.
- Cross-language questions. Many languages are related to each other. A common site would make it easy to ask a question about something that covers two languages. Just add both language tags.
- Cut down on the proliferation of new SE sites. I don't know that having lots of sites is necessarily bad, but sometimes less is more.
- Better search engine results. I can't guarantee this one, but it seems likely. Stack Overflow is always near the top for programming language questions, but I rarely find SE language sites when I search for English or Chinese related questions.
I suppose that everyone is too entrenched in their own communities now to change, but I thought I would suggest it anyway.