Python module for custom MakeHuman plugin not found

Question

I installed a plugin for MakeHuman in it's Plugin folder (in usr/share/makehuman-community). However, the plugin cannot load, since it doesn't find it's own, custom module. I tried out a few different things to fix it: The original line in the __init__.py was: from standardize import * and the folder structure was like this:

└── plugin-folder
     ├── __init__.py
     └── standardize.py

So, since it was in the same folder, I tried just replacing the line with:

import standardize

But that didn't work. So I moved back to the first line and changed the folderstructure to the following:

└── plugin-folder
     ├── __init__.py
     └── standardize
           ├── __init__.py
           └── standardize.py

But still, not working. I have absolutely no experience with python, so I am pretty lost on this one. Any ideas, what's wrong? I think the plugin was written with a relatively old python version originally. Also had to upgrade it from PyQt4 to PyQt5 (in another plugin, but this works just fine. This one here isn't even using PyQt).