[yamtaddle]

It's always the (usually quite bad) tooling, learning about platform/SDK shittiness and pitfalls, and figuring out which parts of the open-source library ecosystem you want to engage with, that takes like 90+% of the time getting decent with a new language, in my experience. Getting comfortable with the language per se takes low tens of hours at most, as you wrote.

[adra]

Kotlin (the base language) is really not that different from java. I went from 0 to standing up new backend services with limited friction. Coroutines and maybe frontends are a different story. Java doesn't yet have a coroutines equiv so that was a larger hurdle for me.

Most of the changes for me from 10/20+ hours to now we're more about identifying a style that works as effectively as I can. These types of behaviours are normal in all but the most idiomatic languages, so if anyone is doing java dev as their daily language, Kotlin felt very natural(though you really are limited to Intellij since the IDE does a ton of lifting to make your life easy).