There are some german files in the directory /usr/share/cups/templates/de which contain the characters
There are some german files in the directory /usr/share/cups/templates/de which contain the characters ä, ö and ü. These characters should be replaced by ä, ö and ü.
Can you please ask the upstream cups maintainers to fix this? Gentoo developers usually only write the ebuild and critical fixes not cosmetical changes. Sorry and thanks for reporting