Do you mean the address? If so, yes, no problem.
If you mean fan letters in English, I don't know - but if the member(s) you're writing to cannot understand English, he/she might ask someone around for translation.
If you're not sure the member understand English, I'd like to suggest to write in plain, simple language, without abbreviations one use on internet (something like "LOL", for instance), keep each sentence simple and short so that your message will be understood well.