"Outlaws anonymous communication by requiring every citizen to verify their age..."
To me that reads similarly to age restricted websites asking you to verify your age before accessing it, where you just input a date that says you're old enough and then you're set. I've been 99 years old for the last decade. Given what they're trying to do, I wouldn't be surprised if they use more extensive verification measures, but I haven't read into that yet. If it's just an age/DOB input, then it's not really outlawing anything.
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.