In the finder, hold down these keys: Command, Shift, G.
In the window that appears, paste this:
~/Library/Application Support
You are now inside your user account's home folder (that's what ~ is), inside an invisible folder called "Library", and inside that folder is a folder named "obs-studio". It is where the application stores all your profiles and scenes.
If you are OK with deleting all your profiles and scenes and starting over from scratch, just throw that folder away and restart OBS. Doing this can address problems like the "failed to find locale/en-US.ini" problem but also problems caused by profile or scene collection files that have become corrupted.
If you think you might want to try and rescue some of those files (like if you have a lot of complex scene collections you don't want to rebuild by hand) move that folder to another location (like your desktop) and then restart OBS.