Where does the Photos app store its files?
It's not as simple as changing the path based on the locale. The Photos library could be renamed and moved anywhere. You can find the current library by extracting the IPXDefaultLibraryURLBookmark from the Photos plist.

/usr/libexec/PlistBuddy -c "print IPXDefaultLibraryURLBookmark" \
~/Library/Containers/com.apple.Photos/Data/Library/Preferences/com.apple.Photos.plist


The IPXDefaultLibraryURLBookmark contains a CFURLRef. This will require deserialising.