How can you write a letter to a friend in German if you don't know how to speak German?

Write it in English and let answer you in German - so both, sender and receiver, have the same effort to learn each others language. Then start the next letter using polite phrases and single words and phrases you’ve learned in the meantime.

What ever you do: Receiving a letter is always a special gift. So do it and don’t mind what happens next.