International Translation Day

A page on the United Nations' site explains:

30 September celebrates the feast of St. Jerome, the Bible translator, who is considered the patron saint of translators.

St. Jerome was a priest from North-eastern Italy, who is known mostly for his endeavor of translating most of the Bible into Latin from the Greek manuscripts of the New Testament. He also translated parts of the Hebrew Gospel into Greek. He was of Illyrian ancestry and his native tongue was the Illyrian dialect.

How did he translate most of the Bible from the Greek manuscripts of the New Testament, one wonders, when the New Testament doesn't make up most of the Bible? And which language's Illyrian dialect did he speak natively?

Anyway, let us party, colleagues!