As the Church in the east chose Greek on the middle age, the Church in Rome chose Latin. On that context, Charlemagne’s contemporary monks, Cirilo and Metodio decided to spread the gospel on the native tongue of their region, Slavic.

That decisions angered Germanic clergymen… and they decide to brung their protest to the Pope, explaining thus their reasons: When Jesus was nailed to the cross there were only three languages on it, Greek, Latin and Hebraic, and therefore those were the only sacred languages. However the Pope (Juan VIII) approved the Slavic experience.
Those debates have little effect nowadays, at least in the Basque Country… as the last scientific researches have proven the Nazaret Prophet didn’t have as a role to inspire any gospel… but the Spanish and French Constitutions… and therefore here Spanish and French are the only sacred languages… because God ordered so.