we have turn a building which was once a bar into a mosque is it alright to pray in that mosque

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

It is permissible to perform prayer in that mosque. It is like all places and there is no evidence for prohibiting the prayer in it. As-Sa‘di said: "All the places of the earth are a mosque (i.e. a place of worship) in which one can offer prayer in them, without any exception, except what was prohibited by Sharee'ah to pray in."

Allaah Knows best.