Nach Ablauf der genannten Frist ist der Anspruch verwirkt, sofern er dem Arbeitgeber gegenüber nicht vorher erfolglos geltend gemacht wurde.
It's actually a fairly simple German legalese sentence. It is easy to understand if you see that it has two parts:
Nach Ablauf der genannten Frist ist der Anspruch verwirkt
Translation: After the end of the forementioned deadline, the claim is forfeit.
Meaning: If you don't make the deadline, you don't have a claim anymore. If you went to court after the deadline, the court would throw the case out without looking at the merits.
unless... - this part is the exception to the rule. German legal texts always follow this structure: First the general rule, then the exceptions or special cases.
dem Arbeitgeber gegenüber nicht vorher erfolglos geltend gemacht wurde.
Translation: was before (the deadline) asserted without success against the employer.
Meaning: If you asserted your claim to the employer before the deadline, the claim is not forfeit even when the deadline passes.
So putting it all together:
Your claims against the employer are forfeit if you do not enforce them before the deadline. Except if you asserted them to the employer before the deadline.
Example: He didn't pay your salary.
- If you go to court before the deadline, you have a case.
- If you go to court after the deadline, but notified the employer before the deadline that he still owes you the salary, you also have a case.
- If do nothing until the deadline (neither notify the employer nor go to court), you have nothing. If you try to go to court after this, your case will be thrown out.