you could basically make libraries, single interfaces and single classes by using module scripts and metatables, but you just have to keep most of your code Flexible, Universal and Scalable if your releasing it to others for use.
localization just helps you keep things local to the players country/region (like language translation for example) I believe, but I don’t think its relevant in this case.
there isn’t really any full blown tutorials on how to make your own library/classes in roblox lua.
I would recommend looking at some of these concepts.
EDIT: if your new to scripting then you’ll probably want to start on something more basic, and I think you mean your wanting to USE the roblox API not make an API for roblox.
you can use roblox API as an interface to influence certain events.
If you mean using discord webhooks, you don’t need to make an API for it. You can simply use HTTPService to signal the webhook. If you mean actual boys, you shouldn’t be using Roblox for not hosting anyways.