Couple of things to double check before giving up:
1. Make sure the VM language packs are installed in the right folders.
( administrator/components/com_virtuemart/languages/ then each folders has to have yourlanguage.php files besides the default english.php file.)
2. Make sure each on of yourlanguage.php files has the right 'CHARSET' set, which can be found at the top of each files code. Like....
$langvars = array (
'CHARSET' => 'ISO-2022-JP',
3. Make sure that each yourlanguage.php file name is in small latter and not like Yourlanguage.php with a capital 'Y'
4. Make sure you have the original Joomla side language installed of your language.
( See publich_html/languages and administrator/languages that they have like for Japanese would be ja-JP folders)
* publich_html/languages is for the front end users and administrator/languages is for the Admin control panel languages)
5 Inside these for example ja-JP folders, you will find a yourlanguage.xml file like for Japanese would be ja-JP.xml open these files and see that line: <backwardLang>yourlanguage</backwardLang> is set right. The language might show like for example <backwardLang>Japanese</backwardLang>, but no need to worry as the capital 'J' letter will be set to lower case when it looks on the VM side and is why you want to make sure your VM side yourlanguage.php files are set to lowercase file names.
6. Once these are all set, then you just have to make sure within Joomla Admin control panel that the default language set is set to your language and should work.
7 One last important this is that you must make sure all yourlaguage.php files are translated in to your language correctly and not just few lines with in the files to make sure it is all showing right and you want to make sure you are using the same CHARSET as the Joompla side language kit you use or else the they will not show up right as well.
Hope this helps some with key points of what to check before you give up.