What to say and what not to say, according to Buddhism

As its said Abhaya Sutta (eg in wiki);

In the case of words that the Tathagata knows to be unfactual, untrue, unbeneficial, unendearing and disagreeable to others, he does not say them.

In the case of words that the Tathagata knows to be factual, true, yet unbeneficial, unendearing and disagreeable to others, he does not say them.

In the case of words that the Tathagata knows to be factual, true, beneficial, yet unendearing and disagreeable to others, he has a sense of the proper time for saying them.

In the case of words that the Tathagata knows to be unfactual, untrue, unbeneficial, yet endearing and agreeable to others, he does not say them.

In the case of words that the Tathagata knows to be factual, true, but unbeneficial, yet endearing and agreeable to others, he does not say them.

In the case of words that the Tathagata knows to be factual, true, beneficial, and endearing and agreeable to others, he has a sense of the proper time for saying them. Why is that? Because the Tathagata has sympathy for living beings.

Here are the wisdom from Samaññaphala Sutta 

I add my ideas in []

Abandon false speech [lies, deceits, forgery, impersonation]… He speaks the truth, holds to the truth, is firm, reliable, no deceiver of the world

Abandon divisive speech [conceit, violence, ill-will] … What he has heard here, he does not tell there, to break those people apart from these people here … Thus reconciling those who have broken apart or cementing those who are united, he loves concord, delights in concord, enjoys concord, speaks things that create concord

Abandon abusive speech [hate speech, violence mongering, generates unrest with patterned attempts to gain control] … He speaks words that are soothing to the ear, that are affectionate, that go to the heart, that are polite, appealing and pleasing to people at large

Abandon idle chatter [gossip; escapism, nothing but takes away one’s meager resources, there are no goals in life but to indulge in wasteful non-beneficial moorings] … He speaks in season, speaks what is factual, what is in accordance with the goal, the Dhamma, and the Vinaya. He speaks words worth treasuring, seasonable, reasonable, circumscribed, connected with the goal.