I would say it took 10 years of professional work across many languages where I can say I feel that comfortable.
Maybe I was a shitty student but I think I went to a general well taught undergrad program that grounded me in the various concepts (although not functional programming and lambda calculus - that was a pure CS-only thing at the time). It took a long time to actually build that level of intuition through experience. I wouldn’t expect someone who is just out of college to have that trait but it is to me a strong signal of seniority (eg you can start helping someone proficient in the language/more familiar with a codebase try to spot tricky system performance issues because you know what kinds of things to Google). Similarly language fluidity is a skill that not everyone develops (due to whatever mix of available time, interest, or natural talent) and that’s also OK. There are plenty of meaningful contributions made by people who only specialize in expressing all the CS concepts in one language and that’s OK too (or even just building useful tools/OSS contributions that are unrelated to CS topics).
Maybe I was a shitty student but I think I went to a general well taught undergrad program that grounded me in the various concepts (although not functional programming and lambda calculus - that was a pure CS-only thing at the time). It took a long time to actually build that level of intuition through experience. I wouldn’t expect someone who is just out of college to have that trait but it is to me a strong signal of seniority (eg you can start helping someone proficient in the language/more familiar with a codebase try to spot tricky system performance issues because you know what kinds of things to Google). Similarly language fluidity is a skill that not everyone develops (due to whatever mix of available time, interest, or natural talent) and that’s also OK. There are plenty of meaningful contributions made by people who only specialize in expressing all the CS concepts in one language and that’s OK too (or even just building useful tools/OSS contributions that are unrelated to CS topics).