A publicity stunt, unlikely to have legal consequences.
- Germany claims universal jurisdiction for cases of genocide. According to the Völkerstrafgesetzbuch §1, this law applies to cases of §6 (genocide) even if the case was committed abroad and has no connection to Germany. For §13 (wars of aggression), it applies whenever the (alleged) perpetrator is a German citizen. So Germany could prosecute any perpetrator of genocide whom they can catch.
- As I understand it, the lawyers did not initiate a lawsuit, they filed a criminal complaint with the authorities accusing the Chancellor of that crime. The prosecution authorities will have to react to this -- almost certainly by concluding that there is no Anfangsverdacht (reasonable suspicion) to justify further steps.
In Germany, most criminal cases are filed by the prosecution. That happens when the prosecutors conclude, in their professional judgement, that a crime has happened and that a conviction by the court seems likely. There are a limited number of crimes where a victim can bypass the prosecution and go directly to the court, but genocide is not among them.
A victim can file a legal complaint if the victim believes that the decision of the prosecution has been wrong (Klageerzwingungsverfahren).