Steps to reproduce:

1. download the German language pack from here
2. apply it to JIRA 4.4
3. exit administration
4. choose German as the preferable language
5. create a couple of issues and link them(eg: link them as duplicate)
6. delete one of the link
7. check the Activity Stream Gadget. It will shows that the 'removed the Link between' in English as below:
   

Please do note that the translation is already accepted as shown in ActivityStreamTranslated.png. The key involved is:

• streams.item.jira.title.remove.linked