Hi,
Let's see how this works...
The language list in download and choose document view is populated in DocumentSelectionBase#populateLanguageList.
It reads all available documents and adds their language to the list.
Languages are translated in the Jsword library, Language:getName.
Language list in JSword is initialized from iso639.properties, which provides
language names in each language (for example fi=Suomi). This is the default if specific file for the language is not found.
There is also iso639_en.properties which gives list of names in format English name (Local name) i.e. for example Finnish (Suomi).
This is used when english language is enabled.