Oh Yes Joerg ! that language problem should really be fixed. I run some softwares in french others in english and my OS is in english. It never causes any troubles...
With VUE, for each update, I have to replace some files here and there. The program is always transformed is a french version ! Once in a while I even get "sonnenlicht" instead of "sun".

Message to e-on :
In the root directory there should be a "preference" file, where all your personnal settings (language and options) are recorded. The updater would read it before doing any modifications. Or, like Joerd proposed it, the updater shouldn't launch itself directly. A little window with "select your language" is a good idea.

There is even an easier solution : make one update application for each language !

Eric