"We speak English."
This is really not acceptable in expressing that we have the ability to speak the language. As Rewjeo said, it really expresses that we sometimes speak English. It could be used in answer to a question such as, 'Which language do you speak at home?'
'Tá Bearla againn' is how it should be stated. The question form would be, 'An bhfuil Bearla agaibh,' - literally, 'Do you (pl) have English?'
So is there 1st person plural pronoun? Is it commonly dropped? Does meaning changed if it is included?
I know in Polish you can say "Mówimy po Polsku" (no pronoun) or "My mówimy po Polsku" but unless it is necessary to stress that "we speak Polish (and someone else does not)" the pronoun is dropped very often.