Antique Large Vellum Church Altar Manuscript / Psalm Leaves

This strangely stiff parchment is double-sided and includes Latin psalms from the Bible. An expert may be better able to explain the particular verses (Google Translate had us stifling laughter at the poor translation on the backside, although the front side was clear).
 
Similar ones online have dates ranging from the 1400s-1500s. We found this amid artwork by Alice Burr who travelled the world in the 1920s and 1930s but we cannot authenticate where or exactly when this came into our family's possession, nor whether it is authentic or not.
 
It is not in great condition, discolored and creased as it was never framed or stored flat.
 
H 24 1/4” x L 17”
 
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