OK, thanks, your Englishness may be the problem then …
I’m saying this, because the error seems to occur in a localization module, and on my system, running in Dutch, and the author’s, who’s French, that module seems to be active, so that on our systems the bindtextdomain function is available. And you need that, to set the path to the translation data, also for English, because the add-on is written in Esperanto.
When you install Gramps in English, it is likely that, because Gramps defaults to English, this localization module is not active, so that this bindtextdomain is not available, unless properly initialized.
This is a wild guess, but it may explain why the author and I don’t see this.
You may be able to test my theory by adding an extra line
locale.setlocale(locale.LC_ALL, '')
above the one mentioned in the error message, meaning at line 142 in PersonFS\PersonFS.py. And since you installed the plugin yourself, you know where that file is.
Note that, in Python, this line must have the same indentation as the surrounding lines, so you need to take care that it has, by adding a proper amount of tabs or spaces at the start of that line.