1) it is more important to be proficient in a problem space (data analysis and statistics, web programming, mobile, networking, etc.) than to be proficient in a

1) it is more important to be proficient in a problem space (data analysis and statistics, web programming, mobile, networking, etc.) than to be proficient in a language, in terms of your actual productivity 2) nonetheless most job postings are in a particular language, so you should do enough in a few different languages that you know the basics of how they work, and know how to look up the rest, so that you can honestly say you have worked in that language, and can get through a basic job interview related to it Becoming proficient in the language's more esoteric edge cases in regards to syntax, etc. is not so important, because that stuff you can look up if you need it. The details of a problem space are often things you won't even know to ask yourself or look up, if you aren't proficient in that problem space. If a prospective employer requires that you know the esoteric details of Golang or Rust in order to get the job, they're probably not a great employer, and there are plenty of others out there who know better than that. The literal answer to your question is 3 or 4.