I've got a discussion with a module vendor (dignuke.com). Here is the text:

The urls generated by article list in a content localization enabled site are different from the standard generated urls. The normal urls look like this:
/nl-nl/colombia/bekendecolombianen.aspx for dutch or
/en-us/colombia/famouscolombians.aspx for english.

the urls generated by the article list module are:
/Colombia/BekendeColombianen/tabid/407/Article/352/language/nl-NL/juan-pablo-montoya.aspx

Is it possible to create the urls more like the standard dnn urls, with the language part at the front?

and his answer:
Unfortunately, it doesn't look like it. The friendly url function in DNN will only format a url like that if only the tab and language are in the url. When you add an additional quierystring value, it formats as your example.
Thanks
Mike

My question is, is it possible to get the url straighten out? Or do i need this to support.dotnetnuke?

Sebastian, it is strange that complete url changes when adding a parameter. I can understand that content localization is not fully complete in 6.1 but and the progress is slow.
But there structure in the urls should be in some sort of formal structure.

If you enable content localization the urls should always start with the language in my opion. The mixing of different url structures is confusing.

I know that i can buy different extensions that will fix a part of the problem. But think for the core it should be important to format a url structure.

ok, maybe in the future there will be a solution from the core.