From Twitter:
A. What's your birth date?
B. Why do you say it that way?
A. Huh?
B. You talk like a government clerk.
A. How should I say it?
B. Good. Say: ''when's your birthday?''
A. OK, but I thought...
B. Forget what you thought; just say: _
* When's your birthday
* What's your birth date
日本語訳
A：生年月日はいつですか？
B：どうしてそんな言い方をするの？
A：え？
B：役所の職員みたいだよ。
A：どう言えばいいの？
B：いい質問。「誕生日はいつ？」って言って。
A：分かった。でも……。
B：考えすぎないで。「When's your birthday?」でいいの。
選択肢：When's your birthday／What's your birth date。
解答・解説
The Answer is as it was instructed by speaker B: When's your birthday?The Explanation is: There is no reason for it except that we speak the way we do. To invent a reason (for people who think language is all rules), let's pretend one is the casual way and one is the formal way (but the real reason is, we just talk that way).
Advice: If you want to learn a language
and use the language naturally,
you have to take a break from the grammar
and use the language, see the language (read!)
and watch native, live productions of the language
(or meet and talk to NATIVE SPEAKERS sincerely, first (because you actually have something in common and want to be friends--not because you need English lessons),
and stop saying ''I'm shy'';
shyness helps no one and is not honorable or helpful--it's just a social dysfunction);
Use the real language in real situations
in real life with real people.
That is how you properly learn how real people use
the real language
in real places.
ここでは When's your birthday? が自然な会話表現です。What's your birth date? はより事務的に聞こえます。筆者は、自然な言い方を身につけるには文法規則だけにとらわれず、読書や実際の会話、英語の映像作品に触れ、相手と誠実に話すことを勧めています。恥ずかしさを理由に実践を避けるべきではない、という筆者の意見も含まれています。