> Different languages have different libraries with different functions that take different arguments and have different data structures. The tools you used with the old language might be different or required modification to work with the new language.

Those are all knowledge differences, not skill differences. Programming is a combination of knowledge and skill, the skill part transfers between languages and environments very well. The knowledge, not always. But learning a new (to you) suite of libraries is not "reskilling". You're not developing a new skill by learning Java's API versus C#'s API.