Ad Scala - it depends if you already knew a JVM based language. If you are coming from Java you will have a head start: use Maven/Gradle instead of SBT, you will already know IJ, you will know your way around managing JVM versions and understand core concepts like jar files and class loading.
For me the most time intensive part of learning a new language is learning the new libraries. I don't mean here the standard library but rather things like library for interacting with SQL database, how mocking works in the new language, how concurrency works, web API framework.
Learning "just" a language can be done over the weekend. Learning to properly use its standard lib and the entire environment of libraries may take years.
The best way to learn a language is to build a project with it. Anything else is just exploring its feature. The trickier issues are always features integrations.
For me the most time intensive part of learning a new language is learning the new libraries. I don't mean here the standard library but rather things like library for interacting with SQL database, how mocking works in the new language, how concurrency works, web API framework.
Learning "just" a language can be done over the weekend. Learning to properly use its standard lib and the entire environment of libraries may take years.