The biblical translation is "render unto Caesar that which is Caesars"

Matthew 22:21King James Version (KJV) 21 They say unto him, Caesar's. Then saith he unto them, Render therefore unto Caesar the things which are Caesar's; and unto God the things that are God's. https://www.biblegateway.com/passage/?search=Matthew+22%3A21&version=KJV

"This biblical proverb..." well, it's not really a proverb. I'd call it a quotation. Because it's from the Bible, you can simply check one of the English translations instead of re-translating from French. One common phasing is, "Render unto Caesar the things that are Caesar's". This is from the American Standard Version. The commonly-quoted translation, the King James Version, simply says "Render to Caesar the things that are Caesar's". I think the "unto" sounds more like a formal declaration. :)

I don't know French, but I know this scripture... Pay back Caesar's things to Caesar, but God's things to God.

Give back to Caesar what it is Caesar's (and to God what is God's).