VS2019: How to resolve the "unknown sub-lang: 0x8" message in Resource View?
This solution helped for me: https://developercommunity.visualstudio.com/comments/96766/view.html
When you have multiple language settings in your Windows, remove all but one. I had to leave the English (US) option. Then the resource opens again without problems. Hope this helps someone (or myself in the future as this is the second time I spend an hour to search for a solution).
The problem is not related to the language setting, but the RC file is stored incorrectly. My file was in ANSI format. As soon as I opened the file with Windows Notepad and saved it as Unicode, I was able to open and edit the resource project in the studio again. (0xFF 0xFE was missing)