Are you sure you’re replacing the right document?
The one included on zip file doesn’t appear to have that statement on line 827; instead, this is the code.
The code that you paste suppose to be on line 850
Try to copy each files on each appropriate location, and make sure that you receive warning saying that you replace your old file with the new one provided on the zip file. I believe you need to backup your old files before you replace it, in case something goes wrong, and you need to use english as the default language, because the manager interface have an additional language for the subsites. If you want to use it in for it language, than open the english language file included, and copy the last few lines containing subsites language array and translate it to your prefered language and put it on the language file for that specific language.
Let me know if you got all the steps done, but still with an error.
I can’t wait to see this working on yours Banzai