There is nothing wrong with 'give me a hand' in this context!

Maybe I'm being pedantic, but I think 'give me a hand' is more appropriate for a physical task, rather than something like helping to learn a language. However, you could use it if you were referring to a particular task, a translation exercise, for example.

Hi! We can help each other, if you'd like to practice. I'm Brazilian, though. Maybe it's better to practice with natives. It's your call, if you feel comfortable with that, let me know :) Good luck with your studies!

I can help you with English if you want me too, but I don't know how to speak other languages except English, and Vietnamese.