Which proper pronunciation? There's church Latin, classical Latin and whatever the music director thinks is correct. No two are the same.
Ecclesiastical (or Medieval) Latin has a completely different pronunciation from Classical Latin as we now understand it. A friend, a few years older than I, attended highschool when the switch was made in teaching back to classical. Thus "civis", pronounced "cheevis" became "key-wis", etc.
Friend accepted it to a point, but then exclaimed to Sister Anna Roberta, "Sister, I refuse to believe that Julius Caesar said 'Waynie, Weedie, Weekie'!"
Gee, thanks Des, I ask a simple question and what do I get? A can of worms,(I'm on a diet, but not That Diet). Hmmm. WWTAU? What would Thomas Aquinas use? I hear he was pretty smart.
I'm guessing Ecclesiastical but now some wiseguy is gonna pipe up with "Well that depends on which Ecclesia."
Oh, and you neglected to say pig latin which I've known since childhood but it adds on an extra fifteen minutes to my Rosary.