The new Extensions system is very flexible - as it is built from components.
In principle there is are "Core Language Packs" which provide the langue files for a core language (eg de-de). Installing a "Core Language Pack" is equivalent to installing a "core-only" language pack from 4.x days.
Then there are "Extension Language Packs" which provide the language files for a particular language and extension. For example if you create a Module - MyModule - you could create a german language pack for the module. The "Extension Language Pack" requires that the Extension (MyModule) has already been installed AND the relevant Core Language Pack is installed.
Now that is the theory, so - if we assume that you want to provide a module - MyModule - for two different culture german and swedish, you would provide the MyModule package, the german language Extension LanguagePack for the module and the swedish Extension Language Pack for the module (3 packages).
As with the legacy module installer the new installer support multiple packages in a single zip - so you could just include all the files in one zip (and make sure that the manifest has three "package" nodes. ie you can package your module and the language packs together.
Lets take it further - assume you created a custom Container for your module - you could include the Container package in the same zip as well. Once we get 5.0.1 out, I will write some more blogs on this.