I just tried to create a multilanguage installation in the current evaluation 6.0.1750.
If I don't activate Show language dialog, I only get the english interface
(Setting the variable %CURLNG% unfortunately, doesn't affect the used language either).

If I activate Show language dialog, then I get the language dialog even in silent mode (/S), which isn't really silent anymore ;-)

And.. shouldn't the current OS locale gets used instead of the default (english) language (if possible)?
A bug?

BTW: Are project files also encrypted in the paid version (version control)?