How to change the language on frontend and backend to language not on list

Good day. I hope someone can help me. I’m a Drupal developer trying out WordPress ??

I need to change the frontend/theme language as well as the backend/dashboard language to Afrikaans(af). How do I go about changing it? I’ve looked at numerous blog post and they all seem to do it differently, some change it in the code and load .mo files where other people say I must use a plugin?

Any help would be greatly appreciated.