How to organize a REST API?

Question

API

I am developing an API for my application. During development, some questions arose:

• The application has many "translatable" entities. For example, in the database there is a table with books "Books" and a table with translations "BookTranslations", which contains the title and description of the book in different languages. What is the best way to implement adding a book in the API?
  
• Application users are divided into 2 parts: regular users and administrators. Should we split the API for these users?
  
• What about methods that are not CRUD?
  

Answer 1

Understood the 3rd question.
For those who are interested, you can see how they do it in Yandex https://events.yandex.ru/lib/talks/2927/.