There is actually a rather recent law in Germany which would make nonconsensual distribution of images which could damage the reputation of a person illegal: §201a StGB [de|en] "Violation of intimate privacy by taking photographs or other images".
This law says that:
whoever, without being authorised to do so, makes available to a third party a photograph or other image of another person which is of such a nature as to significantly damage the reputation of the person depicted incurs a penalty of imprisonment for a term not exceeding two years or a fine.
But even if the person has not already done so, just threatening to commit this crime might also be a crime according to §253 StGB [de|en] "Extortion":
(1) Whoever unlawfully, by force or threat of serious harm, coerces a person to do, acquiesce to or refrain from an act, and thereby damages that person’s or another’s assets for the purpose of wrongful personal enrichment or enrichment of a third party, incurs a penalty of imprisonment for a term not exceeding five years or a fine.
(2) The act is unlawful if the use of force or the threat of harm is deemed reprehensible in respect of the desired objective.
(3) The attempt is punishable.
(4) In especially serious cases, the penalty is imprisonment for a term of at least one year. An especially serious case typically occurs where the offender acts on a commercial basis or as a member of a gang whose purpose is the continued commission of extortion.
Considering the repercussions in the Saudi-Arabian culture and legal system for promiscuity, especially for women, it is hard to deny that there is a threat of "serious harm" in this case.
So it might be a good idea to file a police report with the police of the federal state where the perpetrator lives. The police of most federal states allow to do that through their respective websites (look for the keywords "Internetwache" or "Strafanzeige"), so there is no need to travel to Germany to do so. This does of course require that there is enough information available to obtain the real identity of the perpetrator, which can be difficult with people you only know through online services.
