Translation:There is another priest in the church.
They are both valid English and the Gaelic has several possible meanings: are we asking where he is or who is there? And does the another mean an addition or a replacement? But I don't think the two English sentences have clearly distinct meanings. I think they are both valid, but the 'there' one would be more normal in colloquial English.
Any sentence can have shades of meaning, and I think either of these two would be valid, answering any of four different questions.
1 Where can I find an extra priest?
2 I don't like this priest? Where can I find a replacement?
3 Who is that in the church, next to Father Michael?
4 Who is in the church now that Father Michael has left?
I think the Gaelic and both English translations answers any of these, with yours slightly better for the replacements (2) and (4).
There's no easy way to distinguish (1) and (2) from (3) and (4) in English, but there are ways (that have not been covered yet) to distinguish them in the Gaelic.
So overall, yes, I think that is a valid translation, but they may not have thought about it as this unit is specifically about how to say 'there is' in Gaelic. Have I made it too complicated?
(Note I have assumed the priest is Catholic, and hence male, as there are no non-Catholic priests in Gaelic-speaking areas that I know of, since almost all non-Catholic Christians in these areas are Presbyterian and they don't have priests.) D