Different language for Mac OS and AppStore's softwares My OS X (Mountain Lion) is in English, and I want to keep it like this.

But, for some softwares in the AppStore (not necessary all), I would like to turn it in French when supported (like OmniFocus) because all my colleagues are working in French, and it's hard for me to tell them what to do when they have a problem:

The translator of the software does not necessarily use the same words as me, and it become difficult to navigate through the menus in some cases.

So, is it possible to configure just some software (or all of them as a last resort) to use a different language that the one used by the Mac OS?
Yes! You can launch a single app into any other language with this nifty tool: Language Switcher. I use this all the time when I need english error messages for writing questions on stackexchange.com etc.