Thanks to @Luemmel Filmulator is going to have German translations in the next release.
That said, I did have to widen some UI elements to fit, but even with 50 more pixels of width the text for the last switch still did not fit.
By the way, @Luemmel, there’s one line I forgot to connect to the translation system… here’s the new link to the .ts file: https://github.com/CarVac/filmulator-gui/blob/testbuild/filmulator-gui/qml/filmulator-gui/i18n/qml_de.ts