Schools, diplomas and professors

Once you have made significant progress (you have finished your book and tapes set), you might wish to test your conversational skills with someone that can correct your errors. Or you just might want to ask some things about the language. Unless you're into penny-pinching by trade, I suggest you hire a professional professor for private lessons. Taking a native speaker with no special qualifications is a bad idea that I personally tested for you. You are better off finding a language school which makes the screening (yes, they also take a profit) so that if you're not satisfied, you can ask for another professor. Then just lead the lesson, asking the questions you want, having her repeat or write down on a blank flash card what you did not understand. If you get an old-fashioned, compulsive teacher who wants to teach you her way, by making you write down grammar rules or vocabulary lists from dusty books, get another teacher. I suggest that for such intensive sessions you don't make more than 1:30 hour at a time.

Some people wish or need a diploma to prove their language skills, and I have tried to list the most famous ones for each language.
Keep in mind that you can perfectly learn a language totally on your own, without any professor, just with good books and tapes and then travelling into the country. But it is often very convenient to have someone knowledgeable help you out with the last paint layer.