Rawtherapee 5.3-524 and gimp 2.9.9 on Ubuntu Studio 17.10

Software RawTherapee
3

220/5000
Yes GIMP starts in German, if not started by RawTherapee?
But unfortunately not from Rawtherpee …
Console Output:
(file-tiff: 18925): Gtk Warning **: Locale not supported by C library.
Using the fallback ‘C’ locale.