Make sure that you have installed the hot start package properly. Then add all language packs to Joomla that you need. Do not forget to publish your languages for content! You need to add the missing entries as new items.
Now you have to activate the system language filter (plugin) and then you have to publish the language switcher. I copied the original one in order to have them published on position user2 in both of my used languages german and english. For this, you will have to create menus, menu items, categorys, articles and so on for every language you will use.
Concerning Virtuemart, i had the same problem at beginning. So i did what is explained in my first two paragraphs and than i installed the whole Virtuemart 2 over the existing one. It will act like an Update and will create the missing tables. You have also the possibility to try the Tools in Virtuemart: Refresh and actualisize the Databases.
After all, it should work then.