Re: Is this just an English thing ?
Thee/thou/thy were always the formal version of you/your
'tother way around methinks. The KJV made deliberate use of them to show that God (in the New Testament at any rate) isn't setting himself "above" humanity. I am told that New Testament Greek uses the equivalents. I have no experience of modern languages other than Welsh, but the same is carried forward there. "Thy kingdom come" is talking to God as a friend and in Welsh, "deled dy deyrnas" uses "dy" - "ti", the singular / familiar form of "you" in exactly the same way.
Yorkshire talk uses "thee" and "thou" in that familiar way to this day and it's only the rest of us who promoted / demoted "you" and "yours" to cover both formal and familiar forms that over the years began to believe "thee" and "thou" to be the more formal words, probably because we only heard them used in formal settings such as churches, where the KJV was near ubiquitous up until the 1960s.