本当にありがとうございましたって英語でなんて言うの？

感謝の気持ちを伝えるには色々な表現がありますが、一番平たくて心のこもった言い方は「Thank you so much」だと思います。

「Thank you so so much」でも良いです。

大げさに言うなら「I am eternally grateful to you」（永久的に貴方に感謝をしております）と言うのでも良いですが、ちょっと大げさ過ぎかもしれないですね。

Thank you very much for ... を使って言うことができます。

親切にしてもらったことに対してお礼を言いたいなら、
1) Thank you very much for all your kindness.
のように言えます。

暖かくもてなしてもらったことに対してお礼を言いたいなら、
2) Thank you very much for all your warm hospitality.
のように言えます。

ご参考になれば幸いです！

To express an emotion that is greater than 'thank you,' you can add 'very much' to the end of 'thank you.'

Another way to express this, you can use the verb 'to appreciate.' 'To appreciate' means to feel very thankful.

EX) Thank you so much!
I really appreciate it!

Examples:

Thanks a lot, I really appreciate it!
I really appreciate your help, thank you so much!
You are so kind, thanks for everything that you have done for me!
Thank you so much, I appreciate what you do for me!

You could also add something like ‘you’re a star’, ‘you’re a lifesaver’, or ‘I couldn’t have done it without you’: for example. ‘Thank you so much - I couldn’t have done it without you!’.

If you would like to thank someone by saying more than just "thank you" to someone, you can say something like "I just wanted to say thank you very much for _. I just wanted to let you know that I really appreciated it." or "Thank you so much for everything. I am really grateful for it.".

If you wanted to thank someone by using more than simply thank you, and want them to know you are very grateful, you could say either of the following to express this: "Thank you for what you did, I am very grateful" or "Thank you for the kindness you have shown me".

You can used "very much" to show your gratitude.

You can also say you appreciate the person you are thanking.
"Thank you, I really appreciate your help."

こんにちは。
感謝の気持ちを伝える場合などに、「本当にありがとうございました」は下記のように表現できます。

・Thank you so much.
「本当にありがとうございます」

・I'm really grateful.
「とっても感謝しています」

grateful はありがたく思っていることを伝えるとても便利な表現です。
ぜひ参考にしてください。

Here are three different ways that we can show a high level of thankfulness or appreciation towards someone. Of course we can use, "thank you very much," but I showing your appreciation through saying, "I appreciate it," is an extremely useful way to show your thanks.