Many thanks to the minister friend of mine in Yorkshire who has Nigerian students in his church, and who managed to get me a translation of 'O Happy Day' in Yoruba.

Verse 1 and chorus:

Ojo nla l'ojo ti moyan Olugbala l'Olorun mi,
Oye ki okan mi mayo, Kosi ro ihin naa k'ale.

Chorus-
Ojo nla, l'ojo naa ti Jesu we ese mi nu,
O komi ki nma gbadura, kin ma sora, ki nsi mayo,
Ojo nla lojo naa ti Jesu we ese mi nu

Big thanks to Rev Jev and Amos.