I'm someone who started working on an English-Swedish dictionary around 2015 when I realized my proficiency in Swedish wasn't that great even though I live in Sweden and that it's my mother tongue. English is my second language yet I've spent more time using English most of my life. I'd say the problem I still have with languages is constructing natural sentences, and avoid ones that result in ambiguity without context. I'm trying to learn Japanese since it has been in some parts of my childhood, also because I've been previously taught a bit of Filipino by obligation without my consent.
Note that I might invent words for Swedish because the language lacks its own terminology when it comes to programming, slang words, naming conventions and so on. I've even made a list of problems that occur often in the Swedish language. And my language keeps on deteriorating because I'm not interested in their media, I don't often talk to people, my family won't use new words and etc.
