The encoding of the signature verification audit log seems broken:
@ikloecker wrote in https://dev.gnupg.org/T6869#200690
Apparently, gpg prints the time (zone) with a different encoding than its own texts (e.g. "EDDSA-Schlüssel"). I suspect that a POSIX function is used for printing the time and that one doesn't know that gpg wants to print everything with UTF-8 encoding. We wouldn't have this problem if gpg would use LANG=C. I'm wondering why gpgme doesn't call gpg with LANG=C to avoid any problems with non-ASCII characters.
Note: This screenshot from around Dec 8 2023 in T6869 doesn't have those errors: