How to reproduce: Create/rename an .sr file to e.g. "ü.sr", double-click it, PV will show an error and not load the file. Pretty sure this needs to be fixed in NSIS (not PV itself), since manually opening the file from within PV works fine. Linux has no issues with "ü.sr" either. It's probably just a simple matter of properly quoting or escaping filenames in the NSIS file extension association setup.
Not sure what to do with this one. NSIS doesn't let us specify the supplied file name in the short cut anyway, so the shortcut creation looks ok. No one seems to have mentioned similar issues with NSIS before, either. Only things I could find were https://superuser.com/questions/1301180/cygwin-bash-prompt-here-not-working-with-umlauts and in turn https://github.com/mintty/mintty/wiki/Tips#creating-a-folder-context-menu-entry-for-mintty So might be a Windows issue related to code pages and UTF-8? No idea.