You only need to know the basics of the language to be able to understand average conversations and text. You can also easily express yourself with rather limited vocabulary. The words are ment to be compostable, few basic terms can be used to express any complex information.
With enough exposure and effort you can expand the knowledge of a language with more words. More specific ones that can be used to be more efficient. To a point ot makes sense to expand a language. On the other hand those obscure words make the language more interesting and expressive.
It's not impossible to even the native speakers of such rich languages to come across a word they haven't heard before. But sometimes you just realize you not only know what the word means but also the origins of the usage of the word.
The more specific and weird the word is the more interesting the history of the word seems to be. They become words that not only describe some oddly specific thing, but also reference a piece of history.