Not really. You're right, I should have set my locales to EN as well. But I just didn't think that it might actually be of public interest. I thought qole would use it as a template for a completely new image.

The only thing you should make sure is that it contains no compromising data like your personal VPN login data or something similar.

Another good idea to minimize the size of the compressed image would be to nullify all the empty space in the image. It just did it by creating a file from /dev/zero inside of the image and deleting it. But there's also the Debian package zerofree which should do that even more comfortably.