I don't know if there's an accepted Irish word for posting, in the twitter/Internet sense. Searching mostly suggests people using the English, but that seems disappointing to me when there are such pleasing alternatives.
I think I'm throwing my hat in the ring for ag breacadh, which has a pleasingly wide range of meanings. The root sense is something like "to speckle" or "to dapple", but it's shifted to idiomatically encompass a whole range of things, from dawn (ag breacadh an lá - the day speckling the sky with light) to oats ripening, to hair turning grey (tá mo cheann ag breacadh - my head is dappling). For our purposes, the relevant use is breac síos and tuarascáil a breacadh, meaning to note/jot something down.
I think the invocation of speckling a paper with words carries over the good energy of posting, a sense of mild chaos and randomness expressed by flinging thoughts out into the world.
(Of course, now this invites the question, "how do I find the right version of chosting?" and frankly I do not have an answer right now. I jokingly used "ag chostadh" in an earlier post, but I would love to find something funny and a bit more elegant)