I have set language in MuseScore to Swedish. In the settings menu, one can set the way note names are spelled (Format->Stil->Ackordsymboler->Notstavning). I have set it to Standard which should give me note names like A, Bb, B, C, C# etc, according to the first screen shot. I could also choose the German spelling (Tysk), giving me A, Bb, H, C, C# etc, according to the second screenshot. I prefer the standard one. This will make chord symbols transpose correctly. Transposing Am up one major second gives me Bm, not Hm. But the transposing tool insists using the German spelling for me, see third screenshot.
What MuseScore does here is, it spells note names according to what language I have set the whole gui to. Not according to the setting I chose in Format->Style->Chord symbols. I bet users prefer to set the gui language according to their own language and tone name spelling according to other things.