Writing to a pen pal formal or informal email ?
This is about languages that, in the second person, have an informal and a formal “you.” Would this relationship be formal or informal? I’m asking specifically about German.
The “cut off” level varies enormously, from language to language, and between different generations and different social classes and even between the two genders, within the same language area. The general rule is to use the formal until you are invited to use the informal, but even this can sometimes make you seem so standoffish that no one dares invite you to become more friendly.
In the case of German, I would use Sie, but if I were a teenager writing to another teenager of my own gender, I would use Du, but mention in my first message that as I foreigner I hope I am not giving offence by doing so.
In German one would never address a pen pal the formal way. This is not typical at all. Pen pals are considered friends, you’re often going to share your deepest thoughts with them. Internet language is generally very casual in German, we also use the informal address towards people in forums, chats etc, although they are complete strangers to us.
So write “du”, unless you or your pen pal are already 80 years old. 😉