I speak multiple languages fluently and people are always surprised when I share that my vocabulary is seriously limited. I learned it is an advantage. I am forced to use simple words to explain.
On the opposite end: I had a coworker, I only ever got about 30% of what he said. I thought it's my Japanese skills. He used complicated sentences and words all over the place. But when I asked other Japanese coworkers, they told me they could not understand him either.
If Japanese coworkers could not understand your coworker, is it that he used complicated sentences or that he couldn't use them correctly? Being able to explain things in simple terms is really useful, but it also means that you have to explain a lot more when conveying nuance or precision because you can't choose the word that means exactly what you want to say. Do you ever run into this, or do you feel the simple explanations can cover everything you want to communicate?
On the opposite end: I had a coworker, I only ever got about 30% of what he said. I thought it's my Japanese skills. He used complicated sentences and words all over the place. But when I asked other Japanese coworkers, they told me they could not understand him either.