Why? And what constitutes a “functional language” to you?

Is the fact that they can read, write, speak, and understand the language not “functional” enough for you? The point gets across to the person receiving the message.

You can even translate it to a “functional language” of your choice, with some restrictions. Translation restrictions aren’t isolated to Japanese either, there’s lots of languages that have things which don’t translate well, or at all, to English.