Earlier quoted context omitted.
I believe people over-estimate the benefit of properly learning a language. 3-12 months seems to be sufficient for the specialisation benefits to outweigh the small hit to language competency. My strategy is to be a generalist superficially learning specialized languages.
Whatever time frames you apply, the only way to really learn a language is to use it. Reading a book, blog articles, and watching videos on YouTube won't give you the hands on experience necessary to internalize how everything works.
Day 1: read the introduction of a book, set up editor and environment
Day 2: (superficially) learn flow control and type system
Day 3: practice with coding problems on codewars
Day 4-7: reimplement one of my projects
Week 2: read the second quarter of the book and continue with puzzles
Week 3+: Just projects, maybe invest a day into tooling somewhere in between
That is assuming 1-3 hour days