Apologies for the late response.
と書いて、「反応が遅くてすみません」という意味になります。
I am sorry for the late response.
も同じ意味です。
Responseの代わりにreplyを使って、
Apologies for the late reply.
「返信が遅くなってすみません」
とも言えます。Replyは「反応」ではなく、「返信」という意味です。
Lateの代わりにdelayedを使うことも出来ます。意味は変わりません。
Sorry for the late response. I didn't notice your message.
Sorry, didn't notice.
My battery was dead.
こんにちは。
【Sorry for the late response. I didn't notice your message.】
「返信遅くなってごめん。メッセージ気づかなかった」
上記はほぼ直訳です。
友達であれば（どれくらいの仲かにもよりますが）、LINEなどのメッセージではシンプルに下記のような表現をすることも多いです。
【Sorry, didn't notice.】
「ごめん、気づかなかった」
口語では「私」を意味する「I」は省略しても大丈夫です
【Sorry for the late reply.】
「返信遅れてごめん」
【My battery was dead.】
「電池きれてた」
こちらはよくある言い訳ですね。友達同士の場合はうそでも冗談として言ってもいいですね。
【例】
A: Hey, you wanna go eat tonight?
「今日夜飯いかない？」
-- 12 hours later（12時間後）--
B: Hey, my battery was dead. How bout tomorrow?
「ごめん、充電きれてた。明日は？」
-- 48 hours later（48時間後）--
A: Sorry, didn't notice.
「ごめん、気づかなかった」
B: Sure no prob my battery was dead anyway.
「全然平気おれもずっと電池きれてた」
友人関係の人への返信を想定していろいろご紹介しましたが、ビジネスやフォーマルな場面ではやはりもう少し丁寧な言い方がいいかもしれませんね。
ぜひ参考にしてください。
I didn't see your text. I'm sorry it took me so long to respond!
I missed your text. I'm sorry it took me a while to get back to you!
This is a common problem. All three of these sentences will answer your needs. Each one has two parts. There is an explanation of why it took so long to respond and there is an apology. In all three cases, the explanation sentence ends with a "." and the apology ends with a "!". This puts the emphasis on the apology.
Sorry for the late reply, i did not see your message
I didn't see your message sorry for the late reply
If you didn't see a message straight away then you might have replied back late to someone so it's always nice to say sorry to show you didn't mean to do it
By adding i didn't see your message also shows you were not ignorning them
すぐにメッセージに気付かず、返信が遅れてしまったときは、Sorry と言ってわざとではなかったと伝えると良いです。
"I didn't see your message"（あなたのメッセージに気付かなかった）も、無視したわけではないことを表します。
I did not notice your message. Please forgive me for the late response.
I did not see your message. I apologize for not getting back to you sooner.
Somehow, I did not see that you had messaged me. I am very sorry for not responding to your message sooner.
There are many ways to give an apology. It is okay to acknowledge that you did not notice or read the message at first, therefor making you late in responding. "I am sorry" "please forgive me" "I apologize" are all terms that can be used in English to express remorse and sadness for overlooking something or even making an intentional mistake. These are all ways to express your feeling of being sorry for something and letting your friend know why your response was delayed.
人に謝る言い方はたくさんあります。
始めに、メッセージに気付かなかったと認めて問題ありません。
"I am sorry" "please forgive me" "I apologize"、これらは全て、偶然あるいは意図的にしたことについて後悔の気持ちを表す表現です。
上記例文は全て、申し訳ない気持ち、それに返信の送れた理由を伝える言い方です。
The most common response is, "I'm sorry, I didn't see your message until now."
Please accept my apology for replying so late because I just now saw your message.
I am sorry I didn't reply sooner, I was busy and didn't see your message until now.
最も一般的な返答は、
"I'm sorry, I didn't see your message until now."（ごめんなさい、今までメッセージに気付きませんでした）
です。
Please accept my apology for replying so late because I just now saw your message.
（今までメッセージに気付かず返信が遅れてしまいました、申し訳ありません）
I am sorry I didn't reply sooner, I was busy and didn't see your message until now.
（返信が遅くなってごめんなさい、忙しくて今までメッセージに気付きませんでした）
Sorry I didn't see your message until it was too late.
My fingers fell off, many apologies!
Sorry for not replying sooner, I missed your message.
Ok so let's start with the second one.... This is of course a joke... And sometimes making light of the situation or making a joke is an easy way to apologise without having to make too much of a fuss... saying your fingers fell off means you could not reply via SMS/Text or call - hence your lack of reply to your friend.
You could also let them know that you had missed or not seen their message until later in the same day or the next day. Or you could be direct and say that you did not have time to reply, but some people think this is rude so it is better to say you missed their message. :)
日本 
アメリカ合衆国 
イギリス 
オーストラリア 
