Usage patterns
語彙が豊富だto have a rich/extensive vocabulary
He has a rich vocabulary, so his writing is very easy to understand.
語彙を増やすto increase/build one's vocabulary
I'm building up my vocabulary by studying words every day.
語彙が乏しいto have a limited/poor vocabulary
When I first started learning the foreign language, my vocabulary was limited.
語彙を身につけるto acquire vocabulary
Children acquire vocabulary through picture books.