Generally speaking, I think there are many more greetings that have a
fixed way of saying them in Japanese compared to English. For example,
when you give something to someone, are serving a dish to customers,
or when you meet your children's teacher, or any other time when there
is a fixed way to say something, I think it is safe to say that it is
very important as a member of society to learn those fixed
Breaking it down:
First the speaker gives 3 examples of situations when you would use 決まり文句:
Next the speaker uses the phrase
その is referring back to the 3 examples just given and the
ほか means "other". So, the speaker is now referring to situations other than just explained.
For the next part, you should notice there is a question embedded in the sentence:
Breaking this down further:
- どういう時 > What situation?
- 何と言ったらよいか > What should I say?
Putting them together you get "What should I say in what situation?"
- Next you have が決まっていて which is followed right after the question part. In Japanese, you can have a question form like this be modified.
For example, if you had the question どこで食べますか？ (Where will we eat).
You can also say どこで食べるかがまだ決まっていない (It is still not decided where will we eat)
Applying that to どういう時に何と言ったらよいかが決まっていて you get "It is decided what to say in what situation". However, when translating you probably want to make more natural English, so I made it "a time (situation) when there is a fixed way to say something"
それ here is referring back to the どういう時に何と言ったらよいか that was mentioned previously.
So it is saying "Remembering what things to say in what situation..."
I'm assuming you have no problem here.