Hi, I discovered, that the removal of kde-l10n-de by the package manager also effected packages, which got their own *-l10n-de.
For example libreoffice and firefox-esr now are also in English. I guess, that the removal of kde-l10n-de switched something internally of in kde, so that the other applications are now in English, too. Of course I do not want to delete the whole ~/.kde folder, so it would be nice, if you could point me, where I should look at for a workaround or a fix for the time, this bug is unfixed. Thank you for any help! Best regards Hans