Without additional information:
(As root) "dpkg-reconfigure locales" - additionally select whatever you like, but chose an "en_..." locale as "default".
If it is Siduction's KDE variant: Check all entries in "system settings" -> "regions & settings", that they are not on "German", yes your "Arbeitsfläche" is indeed German, but on English/US settings.
When you change anything you have at least to log out to be sure about settings to take effect. A reboot is even safer

.