When might you say 借你吉言？
承你貴言
http://www.cantonese.sheik.co.uk/dictionary/words/56723/
&quot;wish everything you said would come true&quot;

承你貴言 is a more well known idiom than 借你吉言.
I only heard 借你吉言 for the first time here. It is virtually unknown among Cantonese.
The two phrases are very similar in meaning though,

借你吉言 means &quot;(I hope to)borrow your blessing words &quot;
承你貴言 means &quot; (I) humbly accept your blessing words and hope it will come true&quot;

You can use either phrase as a formal / humble respond, when someone is :

(1.) blesses you good luck

(2.) predicts good fortune or success will come to you.


But I suggest using the more common 承你貴言.