Is there a way to regenerate a missing .resx file?

If you have compiled the project in the past and have the dll/exe available, you can use JetBrains' DotPeek app to export the resx XML from the assembly

Open the dll/exe in DotPeek

Then double-click each resource to see the XML in a window. You can then copy/paste the XML into a text editor and save as a .resx file.

Don't bother right-clicking the resource and trying the 'Save Resource to File' option, as this doesn't create the file in the same format as you see on the screen.

Right click and remove .resx form project right click on form and update resource manager build project run project