At some point years ago I did some online test and it turned out my English language vocabulary was somewhere in the top 0.01% or something like that.

Which is kinda ridiculous because I'm not a native English speaker.

I think it's the result of years of lots and lots of reading things in English: books, newspapers, magazines, even online.

Then on top of that I moved to Britain, which did wonders for learning the local slang of at least the part of it were I lived and even meant some words I learned I only really know them in English (for example, terms used in professional Finance) because I learned them in English, not in my native language.

Also, a lot of the most supposedly sophisticated words are basically the Latin or Greek words barelly changed (sometimes not at all) or technical terms that originated in the dominant language at the time that tech was invented, so they're pretty much the same in all languages I know (so, say, the word "heliocentric" is pretty much the same in my native Portuguese, in Spanish, French, English and so on) so for things like scientific and technical terms having a good vocabulary is mostly language agnostic.