"किसी को मत बोलो।"

Translation: Do not tell anybody.

[JGvXPd]

"Speaking to someone" and "speaking with someone" are essentially interchangeable—both "to" and "with" should be accepted for the "से" in "x से बोलना"

[SyrMja]

Actually, here "se" should be used. With all conversational verbs, except bataana, se must be used instead of ko. So for kehena, bolna, puchna, and baat kaarna use se, not ko. Only use ko with bataana.