Hi Markus,
there's a little problem with your request. The id information in the slug:
488:barrierearmes-joomla-gruendung-einer-googlegroup
Is used by Joomla to understand the article to show. If you drop it how could Joomla knows that information?
docs.joomla.org/Supporting_SEF_URLs_in_your_component
A solution is to create a menu alias (even an hidden menu item) that points to that article. But this could be done for few pages, not for a large number of content.
Another solution is to use ReDJ to create alias. But you must create an item for each alias. This is how you can do (just as example). Suppose that the content to show has the URL:
www.yoursite.com/index.php?option=com_content&view=article&id=488:barrierearmes-joomla-gruendung-einer-googlegroup&catid=13&Itemid=101
And you would like to create this short alias:
www.yoursite.com/barrierearmes-joomla-gruendung-einer-googlegroup.html
Just create an item under ReDJ as follow:
From URL: ^/barrierearmes-joomla-gruendung-einer-googlegroup.html$
To URL: http://{siteurl}/index.php?option=com_content&view=article&id=488:barrierearmes-joomla-gruendung-einer-googlegroup&catid=13&Itemid=101
First try thr 301 redirect and if this works, you can change to interna redirect (Enterprise feature). That's all.
Luigi