You are correct that that is what I think the 1990's ruling. I think video games have changed and perceptions can change on them which could mean court rulings can change. There are two issues you bring up. One Germany's law regarding educational use of historic images (German law & U.S. are different on this issue) and the other are computer (video) games educational under German law. Does German law effect Sweden & Swedish companies? Paradox used to sell physical copies of their game in Germany and those games had to meet German law. Does an international download have to meet German law?
I feel comfortable that my mods meets U.S. law (even if they were for sale (school text books are a commercial product that are educational)) and are uploaded to a U.S. server (I checked). So I am operating in the U.S. and am only subject to U.S. law. Now people in other countries download the mod (very many in Germany) and I don't think they are breaking German law by downloading (even if they paid to do it). Would Germany (the government) threaten a foreign online distributor that if a product didn't meet German standards that they would block Germans (individuals) from access? I think they might if it was overt Neo-Nazi stuff. Not sure on other issues. I know China blocks some stuff I upload, but not in Hong Kong. I cannot meet every countries laws (N. Korea & Iran) and I don't care to.
Disclaimer: I'm not studying Urheberrecht (copyright law) in Germany, but I have some knowledge about it.
German law affects Swedish companies as far as they do business in Germany. So HoI4 could for example not have a swastica in the German version, but the copies sold in all other countries may have swasticas in it. The German lawmaker only cares about what happens in Germany. (As you already said correctly)
Regarding international downloads, it's a bit more complicated. As far as I know, infringement here is not based on the local law of the file hoster (lets say a server in the USA), but on the location of the downloader. So, if your mod is downloaded INTO GERMANY, this mod (or this specific copy of it) now is subject to German law. This certainly affects the user of the mod, but I'm not sure about how it affects you...
In general, German jurisdiction is not really concerned about stuff happening in other countries (unlike the US) as long as no German is harmed. So if what you do is legal in the US (swasticas in mods), Germany won't prosecute you as long as Germany is not concerned. On the other hand, unlawful distribution of copies is also illegal in Germany and some illegal activities may be prosecuted even if they happen outside Germany. Nevertheless, I never heard about German prosecuters trying to prosecute a non-German for something he did in a different country, especially if it's something "harmless" like putting swasticas in a mod, as long as no German was harmed.
To put it in a nutshell: As long as you don't infringe GERMAN copyright holders' rights, you should not fear anything. And even if you do (in a mod to a game that nearly nobody knows, lets be honest), I highly doubt that you would have to fear something. At least as long as it's about pictures taken by people who are long dead. If you infringe a big companies CopyR on music or something like that, they gonna get you^^
Hope that helped
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