I might be in the same boat as you.

I also have a site for English learners and I write all the content in English. All the meta descriptions are in English because I wouldn’t know where to begin to start writing them in other languages.

That said I get a lot of comments and emails from people from non English speaking countries. Maybe they look up their questions on Google in English.

I don’t know about you, but when I think of keywords I just think of the kinds of questions that students have asked me in English over the years.

EG: How can I improve my English in one month?

Things like that.

Anyway, I hope you get some useful answers. I will keep checking in to see what people say.

Thanks for writing the initial enquiry!