My proficiency in them varies. I have used them for projects, such that I can write code in them (provided I have references to read), but when I do, I only learn/use the subset of the language that I need. If I want to read code others have written, then I need to know the subset that they used and that is not always the subset that I know. Most of them are languages that I have used for a handful of projects or in the case of assembly, for very small portions of projects, with at least half of that spend just trying to understand how good of a job the compiler did in critical loops.
There are some languages in which I am extremely proficient. My best language is C, which is my favorite and I have used most features of every version of C from C89 to C11. My second best is probably either C++ or POSIX shell (although I have moments where I forget certain syntax and need to look it up, especially in POSIX shell for variants on variable substitution, e.g. ${VAR%%foobar}). I have used most features of C++98 and some from newer versions. My experiences with C++ have soured me on it, so I now try to avoid C++ whenever I can in favor of C and Python.
My first language was actually PHP 4.2.y, and I was fairly proficient in it, having spent a long time learning it while simultaneously writing my own code for a website as a teenager. However, I never once touched the portions describing objects/classes, namespaces or exceptions. Someone else at work writes Modern PHP code using Symfony and I have taken a peek at it. It looks very different from the PHP I knew because it uses the features I had avoided learning (and probably some new language features too), although I can sort of read it thanks to having learned those concepts in other languages.
I used SML/NJ and Java in college. Years after college, I modified an open source Android TV application written in Java to add some things I wanted, although honestly, beyond that I have not really touched either language. Give me an arbitrary application written in either to improve and I would have some difficulty, although I will probably be able to do it after filling the gaps in my understanding (and doing plenty of head banging if it is a large program).
I have used JavaScript for a few recent projects via electron/nodejs and I have done several small things in Python over the past several years. Each time, I only worked with the subset that I need. I am far from a master of either language that can understand arbitrary code written in them, but I am able to manage as far as my specific needs are concerned.
I could continue listing my experiences doing things in languages (like the time in college that I wrote some basic programs in FORTRAN 90 to try to learn it), but they really are not that interesting. It was often a project here or a small application there, and as I readily admitted, I only used a subset of most of the languages. For programming, a subset of commonly used bits is often all you need.