On top of that there is also understanding the philosophy of a language. Learning python as my 3rd productive language was 3 full-time weeks, "Doing things the pythonic way" took years.

That is also why getting into frameworks is a bit hard for people who are used to do things without frameworks. Like people who stick with JQuery and find Angular hard, because you have to do stuff "Angular way". You can write a lot of javascript and switch to typescript but "Angular way" is yet another thing to learn.

I can write python and understand the code, know some quirks but for large code base I would probably be lost because I don't know "python ways".

This comment could not be upvoted enough. There is a massive productivity level difference between someone who has mastered their expertise in a language's ecosystem and someone who is just coming to the language but able to understand the "linguistics"/syntax quickly (usually because they carry some similarity to an already known PL).

This is not even considering all the little "gotchas" each language will have. Although, Stackoverflow et al. help ease this a bit.