It can be fun to learn other languages through English even if you are not a native English speaker :) You can brush up your English too!

I am Russian and I prefer to learn French mostly through English because they have much in common. What is your native language?

Yes. They are currently making a second "base" language, I think it was French.

Basically I agree with olimo - you can learn new language and refresh your English at the same time. Although it could be a problem if you DON'T know English, limiting user pool.

I've already tried to learn German through English. But I found 2 problems: - Every sentence I have to translate implies a translation in my language then in German. Twice the job. And in high level, it is very complex. - all the "German for English" methods focuse on issues English have with the German language. I have not the same problems with German in my language than in English. Once again, I miss a part of necessary skills.

Although at the end of the day, when you have a good level in a language you can use it as a root to learn another language. But a method in my primary language will be more efficient. Or, like most of the "English as a Second Language" sites do for teaching English, I'd like to learn German IN German (requires a minimum level, of course).

It definitely be perfect to have duolingo for learning every language based on every other, but the number of pairs is very high. I'd say, the first major goal is to have English courses based on more languages and more language courses based on English.

P.S. I am also not an English native-speaker.