Different times for every language. Some I've been able to pick up in a matter of days or even hours (being able to read and write Dart code, for example, was very easy because I already knew Java, C#, JavaScript). Others take a few weeks to feel comfortable (learning OCaml for the first time or getting started with Prolog). Finally, there's a category of languages that take forever to be able to use (namely, Haskell). But each language becomes exponentially easier the more similar languages you know. Learning Haskell after knowing Idris felt like nothing, and switching from Java to C# was a piece of cake. The best way to learn languages quickly is to just keep learning new things. Even apart from learning new abstractions for each language and being able to reuse them, you end up training yourself to think in a more abstract way with more possibilities to work with.