If you were to pronounce "Asperger's" in a German way, I think it would be:
AHZ-BAIR-GGERZZ (with a hard G)
I could be wrong. I didn't take German for long and I learned from a Bavarian.
It would be nice if people used one of the two common pronunciations (Asp-per-Gers with a hard G; or Asp-per-Jers with a soft G). I definitely agree with that. I do not agree with expecting everyone to use the correct foreign pronunciations of foreign words.
I live in the US. Some people here who are fluent in Spanish insist on using the correct Spanish pronunciation of words or names which are also used in English, but with a different pronunciation. For example, burrito. Or Puerto Rico. To say these things "correctly" there is some kind of R rolling and other nonsense going on that makes it hard for English speakers to understand what you're saying. If you speaking one language, just use the common pronunciation for THAT language. Don't make it difficult for everyone to understand you.