Hi,
When you are in the Virtuemart part of your website you have that message :
Missing Flag de-DE for language de-DE.
Go to Extensions > Language Manager > Content, and check the parameter Image Prefix for this language.
Your products are stored for the language "de-DE" and not for the language "en-GB".
The import just find the language "en-GB" but there is no product/categories in Virtuemart for that language ; that's why your import is empty.
The solution is to fix the language in the website in order to allow that "de-DE" language and perform the import with the right parameter.
About the prefix, you can leave the information empty if you are working on the same Joomla site ; that is mostly if you have copied tables from another Joomla in order to import the VM data.
Regards,