My own experience with it is a it more organic and less deliberate, but I find similar things. Once there's a sort of logic to each language that you've acquired it gets easier to learn stuff, the holes kinda fill themselves. I've never reached full confidence -say enough to do a degree in a non-language course- in all my languages but a couple, but there's enough to build on for most of them, and a lot of everyday stuff is okay. I also don't beat myself up over grammatical issues like keeping loads of gender/subject/etc agreements.
On the software side it's maybe similar. You can group languages by various traits like declarative/imperative, GC/manual, static/dynamic types, and a few others. So that allows you to in gross terms translate a program from one language to another, but it's not quite the same as knowing a language inside out so that you fully use all the useful features.