え？って英語でなんて言うの？

単純に聞き取れなくて「え？」という時は下記のようなフレーズを使えます

What??
Excuse me??
(I'm) Sorry??
Come again??

さらに丁重に聞くのであれば
I'm sorry, can you repeat that?
I'm sorry, what did you say?

などがいいでしょう。

どちらもカジュアルな言い方です。

What's that? は語尾をあげていいます。

Huh? は言い方によっては嫌味っぽく聞こえてしまうので気をつける必要があります。

Sorry?は語尾を上げます。

他のアンカーの皆さまがすでにカジュアルな聞き返しについては回答してくださってるので、
丁寧な聞き返しについてあげてみました。

Sorry? はさまざまなシチュエーションで使える、聞き返しの表現。
Could you say that again, please?はより明確に、言い直してもらうよう意思表示しています。丁寧な聞き方です。
Sorry, I couldn't get it. Could you say that again?
はごめんなさい、と謝ったあと、聞き取れなかった旨を伝え、もう一度言ってもらうようお願いしています。

英語を勉強したての時は聞き取れないこともたくさんありますよね。聞き返しの表現にバリエーションを持たせると、何度も聞き返さなければならなかったときに、聞き返しやすいですよ。わからなかったときにスル―せずにきちんと聞く姿勢はとっても大切ですね！

Sorry, could you repeat?
What did you say?
Tell me again.

When your friend tells you something but you didn't hear it, you can use one of these three sentences. The first one, I would say, is the more formal, and generally I would use the second one.

I hope that helps.
Have a great day.
Will

'Say again' is short for 'say it again' or 'say that again'. This colloquial phrase is used to ask for repetition, although it is more commonly used by users of radio communication.

Please note that it may be delivered as an imperative or as a question.

You didn't quite understand or hear something and wish for some clarification or for the sentence to be repeated. Informally,'Uh?' is probably a sound that means the same across many languages.
There are also a couple of slightly longer forms exampled above.

These are two of the smallest ways that we can ask someone to repeat again or show that we don't understand what they said. However, if we want to say something longer we can say :
- I didn't catch that, say again?
- Can you repeat that?
- What did you say?

When someone says something but you did not hear them and want them to repeat themselves; then you may express this in the following ways:
-Pardon?
-Hey?
-Excuse me?
-Huh?
-Sorry?

Huh?
What?
Sorry?
All three are commonly used when you are unable to hear what
a person has just uttered/said. When you use these expressions
then the person automatically knows that you want them to repeat
what they just said. There is no need to say: "Please say that
again." or "Please repeat what you just said." Using "Huh? What?
or Sorry?" would suffice/be enough.

Huh is a common way to let the other person know that you couldn't catch what they said, you can also use: what? Or what was that? These are all informal ways to say this. To say this in a more formal manner you can say: sorry I couldn't hear what you said, could you repeat it for me please?

Huh? What? Come again? Are the short slang type ways to say it. If you want to be super polite you will say something like. "I did not hear you, can you repeat that please?"

If your friend says something and you cannot understand/hear because it is loud, you can say:

-What?
If you say this as you lean toward the person, they will understand that you cannot hear you and repeat what they said louder.

-Huh?
This is a common exclamation that English speakers use when they can not hear or understand something

こんにちは。
下記のような表現もできます。

・Sorry?
「え？」

これは何かが聞き取れなくて、聞き返す時に使える表現です。

・Huh? What did you say?
「へ？なんて言いましたか？」

こちらは「へ？なんて言いました？」といったニュアンスです。
ぜひ参考にしてください。