I am also using Win10, and here's a better solution.
In Gimp 2.8.22:
- Go to EDIT --> PREFERENCES --> FOLDERS (expand this) --> FONTS
- Click on FONTS
- On the right side of the window it will display FONT FOLDERS
- Add your C:\Windows\FONTS folder using the ADD button (icon on the left that looks like a page), and select the folder (open folder icon on the right)
- Press OK, etc. until all the windows are closed
- Exit out of GIMP and restart the application (this is what I did)
Now, you need to add all these FONTS to your toolbox.
- Click on the Tool options triangle at the upper right
- ADD TAB (expand)
- Select FONTS
Check out an image of these menus expanded .
Now all your system fonts should be visible and available for use.