On: every psalm and song in the daily prayers uses today’s English. Off: all of them use the older “thee and thou”. Until you choose, the Songs of Zechariah, Mary and Simeon use today’s English, as most churches sing them. The Lord’s Prayer and the prayers for the dying show the form most people learned.
The doctrine of who Christ is. Lutheran Christology is distinctive in how closely it joins the two natures, which is what makes the Lutheran view of the Lord's Supper possible.
In Doctrine — What Lutherans teach, and where it differs from neighbouring traditions.