The wish is a little fall back option to the english language UI, like GCS worked in the old days before the system language default was integrated. I know currently this can be done with environment variables or java parameters... (something like LANG=en_US.UTF-8 or java -Duser.language=en -Duser.country=US ...)
But for non-technical users and for easier language switching without needing to customize something on every installation, it would be very welcome to include some ready-to-use solution...
Maybe just an included alternative launcher, e.g. named "GURPS Character Sheet (Force US LANG)", that automatically sets the appropriate options to start with EN/US language as a very simple solution without any programming...?
Of course a menu entry with selectable UI language would be even nicer, but IMHO a very quick solution like an alternative en/us-launcher would probably work well for most users.