sales要識既英文

may i know the size u needed? (HK English)
Should be: need.
Or can say: What size are you looking for?
this pants only come with black, blue, brown colour (HK English).
Should be: This pants also comes in Black, blue, and brown color.
like me to mix & match for you? (again HK English)
Should be: Would you like me to match it for you?
fitting room is that way
Or Follow me, the fitting room is this way.

One moment please
can also be:
Take one second please
Will be right back

Line up for the fitting or cashier.

Sorry this item is out of stock, would you like to look at this instead?

Would you like to leave your number?
When this item is back ordered, we can called you once they come in?

There's no exchange or refund during final sale.

welcome to XXX (牌子名)good morning Sir / Madammay i help u?may i know the size u needed? one moment pleasesorry we don't have M size. would u like to try L size instead? this pants only come with black, blue, brown colourlike me to mix & match for you? fitting room is that wayplease queue up here for fittingthank you, please come again

Your question is too abstract but following is some examples.

Good Morning/Good afternoon/ Good evening May I help you Sir/Madam!

Please let me whenever you need help.

Thanks for coming. Goodbye!
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如果可以清楚說明你需要的句子, 我們可以更準確地轉成英文o
If you let us know what you would like to say, then we can be more helpful