Vocabulary is the first test of the interpreter. When a witness in a patent dispute says a substance sublimates, the interpreter either knows the Japanese word (昇華する = shouka suru) or doesn’t. Early in my career I interpreted an important meeting at which a Japanese company was to announce its decision either to abandon or continue with a joint project. After a long preamble, the Japanese executive gave his one word answer: zokkou (続行=continue). Unsure if this was a yes or a no, I was reduced to delicate probing for alternative expressions (not wishing to say “what does that mean?”). That time I squeezed by.
Since then I’ve made a practice of writing down every new word I hear, adding these words to a database which I now manage online. Some are common, some more exotic. But I’ve heard them all in conversation, so I can vouch that they’re not dead words or merely the obscure quarry of scholars and writers. I encourage fellow lifelong students of Japanese to try them out for size.