The handling of the language of the core component is a little bit special. There is no ini file in the Joomla language folder. But you find the language in a special language folder inside the components folder and you can do your language overrides by copying this folder and modifying the language strings. There is no possibility to do this in the Backend. This is not the Joomla standard. On the other hand the ini files of the modules are in the Joomla language folder and can be overwritten.
Four stars, number five is coming as soon as the component has the Joomla standard language handling. But this will for sure take a lot of work to do.
Virtuemart 2 is my first choice and I can recommend it to everybody who is looking for a well working shop system in Joomla 2.5.