Our themes make use of
language packs.. I'm not aware of any reason why they wouldn't work on a ClassiPress installation that is part of a multisite setup as the .mo file is just dropped into the theme folder and the
wp-config file is edited to use that particular language.
I don't know what you're asking specifically regarding changing the language, but to be clear, these language packs allow you to change the theme into another language, but are not going to give you an automatic way for the site visitor to change the language from the front end i.e. multilanguage option.