There's a quote, cited as a proverb on Google:
"Don't speak unless you can improve upon the silence." - Author unknown
In the first page of results, I saw it attributed as a Spanish proverb, a Mexican proverb, a New England proverb, a Chinese proverb, and a Vermont proverb. I've got no idea where it comes from. (I wonder if my filter bubbles prevent me from finding good sources?) It's always kind of rubbed me the wrong way, because I'm not particularly fond of silence. I particularly dislike spending time with someone who insists upon periods of silence between you out of a sense of the a priori value of it. I mean, sure. If it emerges naturally, and you enjoy it, it's not entirely unreasonable to assume the other people keeping their mouths shut are enjoying it too. But I don't want to hang out with someone just to stand there while they think to themselves about whatever. If I want to be silent and hear silence, I can do that at home. (Where I probably won't, I'd rather put on some music and read or watch TV.)
Thinking about it, though, it's usually irritating to me when I'm hanging out with someone whose conversation I appreciate, who I know is worth talking to. There are definitely people I'd rather just hear shut up than listen to them keep talking. Listening to those people can be even worse than listening to my own thoughts and nagging boredom.
So, I propose a substitution:
"Don't speak if what you have to say is even worse than silence." - T.X. Watson