I am proficient in about a dozen languages, but only use 3. I go back to the SPS, PL1, Fortran, and COBOL days, and would rather chew razor blades than ever use them again. Today, I use javascript on the client and php on the server; I have yet to find a problem I couldn’t solve with them.
In the years in between I discovered BASIC and have found it to be the Swiss army knife of apps. Not the old Dartmouth Basic, and certainly not anything Microsoft bastardized, but there are many other versions that seamlessly integrate with relational data bases that I think are a dream.
It’s actually reached the point where I “think” in BASIC, design my app, and then sometimes write in in javascript or php.
I certainly wouldn’t recommend my approach to someone else, but I think that’s the whole point. Use the right tool for the job and get good at it. I see no need to learn new languages just for the purpose of learning something new. If I get “curious” or want to expand my mind, I can think of several hundred app problems waiting to be solved in any language, take your pick.