Thanks for the tip with the unicode flags for tags.
🇨🇳, 🇩🇪, 🇪🇸, 🇫🇷, 🇬🇧, 🇮🇹, 🇯🇵, 🇰🇷, 🇷🇺, and 🇺🇸 work and look really great as tags. (EDIT: apparently it is platform dependent, so e.g. windows users don't see those as flags by default. )
I just haven't found out how to mention such a tag.
#🇩🇪 does nothing.