How to write this very simple plugin?

I want to use my own language package, not from trasifex. I tried changing the Dockerfile of overhangio/openedx image and copied my lang folder into /openedx/locale directory and rebuilded it. But something strange always occur, causing lms can’t work in development mode.

And I want to know how to write a plugin to achieve this. I searched some knowledge about python’s entrypoint, and I know I can start my plugin by cookiecutter, but I don’t know anything else, especially how I can make my language into tutor by plugin, or what else knowledge should I learn to handle this? Thanks in advance.

Have you made some progress with this? Do you still need help? What did you try?