I've given this about 45 seconds thought, in the spirit of an interesting problem that's not my problem. If I had this problem, one thing I would try would be

I've given this about 45 seconds thought, in the spirit of an interesting problem that's not my problem. If I had this problem, one thing I would try would be to find language schools or teachers in the target language, located in your current country (for ease of logistics). For languages that can't be helped in your country, I would look for English schools or teachers (or whatever your target language is, if not English), in countries that use those missing languages. The more developed the country the better. No clue on how to set payment, but I guess that depends in part on whether/how much you expect to make from your project, or more vaguely how important your project is to you.