Apple - Is there some kind of certification for Apple developers?

There is no official certification. There are, though, non-Apple-official courses which are highly reputed, such as Big Nerd Ranch's, for instance.

Apple now offer training with software engineering focused courses for Swift and iOS:

App Development with Swift

Swift is a powerful and intuitive programming language for macOS, iOS, watchOS, and tvOS. Writing Swift code is interactive and fun, the syntax is concise yet expressive, and Swift includes modern features developers love. Swift code is safe by design, yet also produces software that runs lightning fast.

With regard to Apple certification, they do not offer software engineering specific certification.