I'm a native English speaker, who is attempting to learn German. I've been having an email conversation with a German customer who wrote to me in English. I would like to make some small, friendly gesture, like maybe ending an otherwise English-language email with "mit freundlichen grüßen". Would a typical German person find that weird/offensive? (Or maybe, hopefully, a nice gesture?)
I consider myself a typical German person, and as such I find adding some kind words in the mother tongue of the recipient a nice and friendly move. I do this myself almost always in my correspondence with project partners in other countries. Similarly, my project partners do this vice versa.
PS: Aber es wäre noch besser, dabei auch auf die richtige Schreibung zu achten: Mit freundlichen Grüßen - achte auf die Großbuchstaben!