I made the changes to my post
unfortunately that was not what I asked for - for example your screenshot of the filepath begins with "this pc", not with the drive letter.
There are several folder above "documents" if you go through the filepath itself, and I wanted to check if there is any problem in the paths.
Problems like the space in "hidden heros" that have to go, because you will get deployment errors if any part of the filepath contains letters or symbols that are forbidden under networking rules (like spaces are not allowed).
That said, your problem has nothing to do with your project, but with the editor in steam.
I edited my first post, and that is part of what you now need to do to check.
1) go to steam help and search for the instructions on how to clear the download cache. That is prominent there because it is a known problem. After you find it, follow those instructions to clear the cache.
2) deinstall the editor through steam, restart your computer and then reinstall it after the restart. Do NOT test it yet!
3) Launch steam, right-click on the MV editor and open the program properties.
4) go to the language tab and check which language is set there. If it is set to something other than english, set it to english.
If it is set to english, set it to any other language, press OK and wait for the download to finish, then set it to english again.
You do not have to use the different language, I just want to force the mechanism of redownloading the correct language files because the error message is about an empty locale filepath, and "locale" is the file that handles the language settings.
5) once the last download is finished, try to launch the editor and check if it is now working.
If not, we really need the full filepath to your project as an error there is the only thing that could block the editor by blocking it from loading.