French phrase
Dites-lui que ~.
Meaning
Please tell them that ___.
When to use it
A polite request to pass on information. It is natural when the person's gender is unknown or unstated.
Example dialogue
Dites-lui que je ne pourrai pas venir demain.
Please tell them that I won't be able to come tomorrow.
D'accord, je lui dirai.
Okay, I'll tell them.