As a British native English speaker, I would not say "happy Saturday". It sounds American to me - along the lines of "happy holidays". A Britsh speaker is more likely to wish someone to "have a great weekend" or "enjoy Saturday". To which we would reply "Thank you! Have a good one as well.", "Thanks - same to you!" or "Thank you - have a great Saturday too." However, as mentioned by another teacher, if some did say "Happy Saturday" or "Happy Sunday", I would understand the sentiment behind it.
イギリス英語のネイティブスピーカーの私は"happy Saturday"と言いません。アメリカ英語の "happy holidays"にきこえます。
イギリス英語は "have a great weekend" や "enjoy Saturday"といいます。それに対して "Thank you! Have a good one as well.", "Thanks - same to you!" や "Thank you - have a great Saturday too." といいます。
しかしほかの講師もいいますように"Happy Saturday" や "Happy Sunday" でも伝わります。
have a good one as well = あなたも[良い1日を](https://eikaiwa.dmm.com/uknow/questions/56332/)
same to you = [あなたも](https://eikaiwa.dmm.com/uknow/questions/56995/)
Well, 'Happy Saturday' seems like a strange expression for someone from the UK, but the meaning is clear however.
"Hey Mark! I haven't seen you in ages!"
"Yeh, I've been travelling round Europe theses past 3 months."
"Wow, that sounds marvellous. Where did you go?"
"Paris, London, Madrid, Barcelona - you know, the usual tourist destinations."
"Well, I haven't seen any of those places....maybe one day!"
"OK, sorry, I have to run. Happy Saturday!"
"Same to you!"
Happy Saturday' はイギリス出身の私にとっては不自然にきこえますが言いたいことは理解できます。
（英文）
"Hey Mark! I haven't seen you in ages!"
"Yeh, I've been travelling round Europe theses past 3 months."
"Wow, that sounds marvellous. Where did you go?"
"Paris, London, Madrid, Barcelona - you know, the usual tourist destinations."
"Well, I haven't seen any of those places....maybe one day!"
"OK, sorry, I have to run. Happy Saturday!"
"Same to you!"
（訳）
「やあ、マーク。長いことあっていないね。」
「そうだね。この三か月間ヨーロッパ周辺を旅行してたんだよ。」
「[すごい！](https://eikaiwa.dmm.com/uknow/questions/1165/)どこに行ったの？」
「パリ、ロンドン、マドリッド、バルセロナ、観光客に人気なところに行ったよ。」
「私は行ったことないけどいつか行ってみたいな！」
「ごめん、そろそろ行かないと！Happy Saturday!」
「[あなたもね！](https://eikaiwa.dmm.com/uknow/questions/21220/)」
▪Thank you, the same to you.
▪Thank you, have a great Sunday/Saturday as well.
as well=with equal reason
Example 1
Friend: Happy Sunday.
You: Thank you, the same to you.
Example 2
Friend: Happy Saturday.
You:Thank you, have a great Saturday as well.
▪Thank you, the same to you.
▪Thank you, have a great Sunday/Saturday as well.
as well=同様に
【使用例1】
友人: Happy Sunday.（よい日曜日を）
あなた: Thank you, the same to you.（ありがとう、あなたもね）
【使用例2】
友人: Happy Saturday.（よい土曜日を）
あなた:Thank you, have a great Saturday as well.（ありがとう、あなたもよい土曜日を）
Firstly, it is good manners to thank the person wishing you a happy Saturday/Sunday. Secondly, it is good manners to return the good wishes because its a foregone conclusion that he/she is also looking forward to a happy Saturday/Sunday.
So, you may say:
Thank you. Happy Saturday/Sunday to you too.
or
You may simply say:
Same to you!. Enjoy!
まず最初に良い土曜日/日曜日をと言ってくれた人にお礼を言うことは礼儀正しいことです。
次に相手も又良い土曜日/日曜日を望んでいることは言うまでもありませんので、祝福の言葉を返すことは礼儀正しいことです。
こう言うと良いでしょう。
例文
Thank you. Happy Saturday/Sunday to you too.
ありがとう。あなたも 良い土曜日/日曜日を
シンプルにこう言っても良いでしょう。
例文
Same to you!. Enjoy!
あなたもね！！楽しんで！！
When someone wishes you well, then you can say "you too" after thanking them. Or you can say "I hope you have a good one too".
For example:
Person one: Have a great Saturday
You: I hope you enjoy yours too / I hope you have a good one too / You too.
誰かに楽しんでなどと言われたときは、感謝の気持ちを込めて "you too" （あなたもね）と言うといいでしょう。または、"I hope you have a good one too"（あなたも素敵な土曜日を）というのもいいでしょう。
例：
Person one: Have a great Saturday
相手：土曜日楽しんでね！
You: I hope you enjoy yours too / I hope you have a good one too / You too.
あなた：あなたも楽しんでね/あなたも楽しんでね/あなたもね。
examples
"Have a good break from the working week"
or " Have a great weekend"
or
"Enjoy your weekend off"
or
"Have a great break, enjoy the weekend"
"Have a good break from the working week"
仕事お疲れ様。よく休んでね。
" Have a great weekend"
素敵な週末を。
"Enjoy your weekend off"
楽しい週末を。
"Have a great break, enjoy the weekend"
ゆっくり休んで、楽しい週末を。
こんにちは。
下記のような表現が使えます。
・Happy Saturday to you too!
「あなたも良い土曜日をお過ごしください！」
・You too!
「あなたも！」
相手にも Happy Saturday と返したり、シンプルに You too と言うと自然です。
最初に Thank you と加えるのも良いかもしれません。
ぜひ参考にしてください。
You can respond to this by simply saying the same thing back and adding “to you too”.
Another way would be wishing the other person a great day.
Example:
A: Happy Saturday!
B: Thanks! Have a great day!
これはシンプルに、相手の言ったことを繰り返して、その後に“to you too” と加えればオッケーです。
他の言い方として、「よい一日を」と返すこともできます。
例：
A: Happy Saturday!（素敵な土曜日を）
B: Thanks! Have a great day!（ありがとう、よい一日を）
First two are a more simple way of replying to the phrase "Happy Saturday/Sunday", whereas the third way is a bit more polite and I would recommend using the third one.
イギリス 
日本 
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アメリカ合衆国 
