To add support for a new language, first of all you need to create a fork of the project.
Next, create a copy of the file custom_components/huawei_mesh_router/translations/en.json and give it a name <your_language_code>.json. The new file should also be located in the custom_components/huawei_mesh_router/translations/ folder. After that, translate all the values in the json file into your language.
Note: The language codes follow the BCP47 format, a few examples can be seen here.
After that, you will need to make a pull request to the original project, I will check it and add your language to the list of supported.
Download the en.json file, translate all the values into the language of your choice, and create an issue to add a new language.
Be sure to attach the translated file to the issue and specify which language it is, so that there are no misunderstandings.
After checking, I will add a new translation to the component.