I have a question, I’m studying Swift because I want to be an iOS app developer. When I was studying Web, Back-end was Node.js and Front-end was React.js. Then, What is iOS back-end language? I don’t know that.
>Solution :
Assuming with "back-end" you mean a server or API that provides data or functionality.
This isn’t related to iOS at all, you can use the same backend API in Android, iOS, Web and other apps. There is no convention or best-practice on the language to use.