You have to know certain words to have more complex thoughts.
The word "fear" has other so called synonyms but actually
Dread
Unsettled
Spooked
Terrified
Shocked
Startled
And SOHH many other words are similar, but have different shades of meaning.
If I tell you I was happy, vs delighted, vs amused, vs content. They all mean slightly different things.
If you are not well read then you might not even know the particular word or might not know the difference between words.
I imaging knowing different languages gives you an even deeper well of nuances and meanings. I only know American English but as an Ugly American, I consider it superior and wholly efficient. American English actually includes "foreign" words. We all know the difference between manga, comics, cartoons, and anime.
Summary. I use the words my audience can grasp. If I realize the person doesn't understand "nonplussed" I'll break it down to "not real happy".
Vocab and language is the crux of our human super power. Those that don't know the language well are literally unable to think higher thought.