At the time Paul was around, there already WAS a Greek translation of the Hebrew books of Moses - and probably some of the prophets, as well. Ever hear of the Septuagint? Your "obviously" isn't obvious at all!
>> “At the time Paul was around, there already WAS a Greek translation of the Hebrew books of Moses” <<
.
And Paul, being a student of Torah, knew that it was of no consequence, since as he stated, the oracles of God are committed only unto his people.
The Greek translation was unreadable by Greeks, due to its Hebrew syntax. It was written for Hebrews in Egypt.