It may have something to do with a wrong configuration file. There should be some tables like product, manufacturer, category or order with _de_de or _en_en. VMLANG is just the variable name which is called to show the selected language.
So the table name should be: reisesim.fvu03_virtuemart_categories_en_en or if a second language there should be a second table like:
If it only shows VMLANG the VMLANG variable does not find any language table. You can take a look into the mysql database with phpmyadmin to see if there are language tables. If there are tables, it must be a configuration error in Virtuemart, else somthing went wrong with the installation. By the way, does VM use mysqli or mysql?