For handling text I'd go to try the InDesign forum, where various aspects of "language" have been discussed. There are ways to change the interface language, but that's a very different issue from applying the correct spelling dictionary or hyphenation rules to a piece of text: English-language ID, for example, comes with dictionaries for many other languages, which can be invoked via the language attribute.
Edit: Almost forgot a very useful node over on Typophile for users of CS6.
If you talk about the programs, it is not possible without hacks for creative suite software. If you are using the creative cloud, and have separate profiles on a mac, each in its own language, you can do it: