Installation seemed like it went fine until I opened the app, and many of the onscreen menus for selecting colors, etc show gibberish (fractions?) where there should be dialog box text?  Tried reinstalling several times using available versions, but nothing works.

I´m too still on High Sierra - runs pretty well so far. Do you have any former versions installed? Reinstalling won´t help much methinks. There´s a little tool called AppCleaner.app which collects all parts Inkscape installed. I recommend to find these files with the help of this tool - then localise the Inkscape preference.xml file and delete this. Restart Inkscape and see if this helps already. If not trash Inkscape and all findings completely and install again. Good luck.