The Christian faith is founded on the Hebrew Bible and additional Christian books that make up our Holy Scriptures, yet too often our doctrines have arisen from mis-translations of the original languages these texts were written in. Here are a few examples:
El Shaddai (אֵ֣ל שַׁדַּ֔י)
One of the labels for God in the Hebrew Bible, El Shaddai has been (mis)translated as "God Almighty" since the pre-Christian translators of the first Greek Old Testament (the Septuagint) mistakenly thought that "Shaddai" came from the root shaddad that meant "overpower" or "destroy." This pattern was followed in Jerome's first translation into Latin with the Vulgate as Omnipotens which is our root for "omnipotence."
Today Jewish rabbis point to Jacob's blessing in Genesis 49:25 to show how El Shaddai is paired with a different root word, that for the breast of a woman (שַׁד). Rather than the connotation being of an omnipotent deity, here we would understand El Shaddai as "God of Sufficiency and Nourishment" as in the one who promises to multiply Abraham's offspring (Genesis 17:2).
El Shaddai means God Nurturer.
This phrase is traditionally translated "Kingdom of God" (Matthew uses the alternative "Kingdom of Heaven"). However, the Greek basileia simply indicates any politically defined region. This could be a kingdom, but is not required by the word. Since Jesus spoke of God in intimate familiar terms as "Abba" (linguistically similar to our "Dada", "Mama", or "Papa"), we could understand this phrase as intimately as "Home of Papa." And given Jesus's aggressive reinterpreting of leadership as servanthood and equality, "Divine Commonwealth" would be another good translation.
Rather than Kingdom of God, the Gospel is that the Home of Papa or Divine Commonwealth has come near to us (Mark 1)!
Many Christians have understood the Gospel as offering "eternal life," and often assumed this to be speaking of a post-death experience. However, the phrase translated "everlasting" or "eternal life" is anionos zoe which has nothing to do with unending life. It's speaking literally of an "age" or "eon" (from the Greek "aon"!) which is defined as having both beginning and end.
If the authors of the New Testament wanted to talk about unending eternity they could have used αἰδιος (as Paul does in Romans 1:20), but when talking about the life offered in God they spoke of αἰωνιος — a subtle but vital difference.
Many scholars say this phrase is intended to denote quality more than quantity of life: this is "life of the age of God". Jesus came to offer us "life that overflows", life in all its fullness, abundant life (John 10:10).
It's not eternal life, it's Life of the [Commonwealth] Age or Life Divinely Saturated.
(Related: Matthew 25's "everlasting punishment" is more literally "age of pruning/correction.")
* Thanks to John Cobb's "Jesus' Abba" for pointing some specifications around the first two of these mistranslations.