I'll tell him/her/it
I won't tell him/her.
Se lo diré a Tom.
I'll tell Tom.
A usted también le puse un apodo, pero no se lo diré porque estaba equivocada.
I gave you a nickname too, but I won’t tell you what it was because I was wrong.
— Vivir (1952)
I'll tell everyone.
Se lo diré al abogado de tu yerno.
I'll tell your son-in-law's lawyer.
Basta, pórtate bien o se lo diré a tu padre.
That's enough, behave yourself or I'll tell your father.
— Cuentos de Tokio (1953)
Se lo diré cuando tenga un país.
I'll tell you when I have a country.
I'll tell him tomorrow.
I'll tell him.