So I was taught the difference between 唔該 (m goi) vs 多謝 (do ze) today. Both of these are used in Cantonese dialog and hardly used in text.
Both of these mean thank you and personally I’ve always used them interchangeably, but was taught the difference between them today. Apparently if money is ever involved, you should use 多謝. 唔該 is usually reserved for something small, like assistance provided. I asked if there’s ever a situation where you can use 唔該, but not 多謝. They agreed that 多謝 can be typically used wherever 唔該 is accepted, but not the other way around. So when I said 唔該 after getting treated to dinner, it was used incorrectly. I should have used 多謝.
I asked them how to write 唔該, since my Cantonese dialog to text is weak. Usually I ask my father these questions. Like the other day, I asked him how to write poke a hole. In text/Mandarin (the Chinese I learnt), it’s completely different. I forget why I asked him how to write poke a hole, but it’s 篤個窿 (duk go lung). Speaking of which, CantoDict is an awesome Cantonese Dictionary if you’re ever interested in learning Cantonese.
After seeing the kanji, I began breaking the word apart. First, 多謝 means many thanks. 唔 means not and 該 means should. In other words, 唔該 means you shouldn’t have, which I guess can be interpreted as thank you. I’ve been using this phrase for who knows how long and it’s the first time I realized the meaning. Chinese is so fun sometimes!
Update： Thanks to superekin for providing an extra point of view. He said to think of 唔該 as どうも (doumo) and 多謝 as ありがとうございます (arigatougozaimasu).