We are planning to make a portal using some plugins

Hello,
We are planning to make a portal using some plugins (membership, coursepress etc.). Website will be in two languages – English and one more(probably polish). In future we may add some more languages. Portal in English and Polish language would be most same, but with some small differences. F.e. they would use different payment gateways. Probably some more small differences we can see in future, but don’t plan nothing serious at this stage. I wonder if you have any plugins which would allow us to build multilanguage site using your plugins and themes, with ability to switch languages by user(something like WPML). Or maybe you would recommend make separate installations for this two languages for easier management of both sites.
Will be grateful for answer,
Regards, Damo