The Blessed Buddha once said:
How, Cunda, is purity of verbal action fourfold?
1:
Herein, one avoids lying, abstains from false. He speaks the truth,
is devoted to the truth, reliable, trustable, never deceiving anyone.
Being at a meeting, among family, in society, or in the court called
upon and asked as witness to tell what he knows, he answers, if he
knows nothing: I know nothing; & if he knows, he answers: I know!
If he has seen nothing, he answers: I have seen nothing & if he has
seen something, he answers: I have seen this and that. Thus he never
deliberately speaks a lie, neither for his own advantage, nor for the
advantage of others, nor for the sake of any trivial gain whatsoever.
2:
He avoids divisive speech, spreading rumours, tale bearing, & gossip.
What he has heard here, he does not repeat there wishing to cause
dissension there by splitting those united. What he has heard there,
he does not tell here so to cause conflict by splitting friends here..
Rather he unites those who are divided; and those who are united
he encourages. Harmony, peace, agreement & concord gladdens him.
He delights and rejoices in Harmony. He spreads & grows Harmony!
3:
He avoids harsh & aggressive language, he abstains from all scolding.
He speaks such words that are gentle, soothing to the ear, pleasing,
heart-touching, polite, dear, considerate, interesting & agreeable..
4:
He avoids vain talk, empty & small talk, void speech and idle prattle!
He abstains from all babble, chitchat, tittle-tattle and evil hearsay.
He speaks at the right time, in accordance with facts, speaks what
is useful, speaks about the Dhamma and the Discipline; his speech is
like a precious treasure, well timed, always reasoned by arguments,
moderated, well formulated & full of sound reason & common sense.
In this -for all- very good way, is purity of verbal action fourfold!
Source (edited extract):
Numerical Discourses of the Buddha. Anguttara Nikāya AN 10:176
http://What-Buddha-Said.net/Canon/Sutta/AN/Index.Numerical.htm

More on Right Speech (Sammā Vācā):
http://www.accesstoinsight.org/ptf/samma-vaca.html
http://What-Buddha-Said.net/drops/IV/Not_Splitting.htm
http://What-Buddha-Said.net/drops/IV/Not_Scolding.htm
http://What-Buddha-Said.net/drops/IV/Not_Deceiving.htm
http://What-Buddha-Said.net/drops/IV/Not_Gossiping.htm
http://What-Buddha-Said.net/drops/What_is_Right_Speech.htm
http://What-Buddha-Said.net/drops/IV/Fourfold_Right_Speech.htm

and Animal-like Talk:
http://What-Buddha-Said.net/library/DPPN/wtb/s_t/tiracchaana_kathaa.htm
Sweet Speech!