I have never found an oath or any documentation where Christoph was naturalized. My hunch is that he wasn't. In "A Hessian Diary of the American Revolution," author and soldier in Christoph's A-B Regiment, Conrad Dohla, states that Christoph planned to remain in Frederick where he wished to marry. Another source says that he was "promised a congregation." It all fell through and he accepted a large land grant with his fellow Hessians in Nova Scotia. Within a few years, he "ran afoul" of the Anglican Bishop there and left. Official word was that he planned to return to Germany, but I, along with the late John Merz, Hessian expert, feel quite certain that he and his wife from Maryland returned there, residing near Oldtown, Allegany Co. It's a fascinating story.
He was originally the Chaplain for the Bayreuth Regiment, if I understand correctly, therefore most likely hailed from the Bayreuth region. Not amazingly helpful to know that, but it narrows it down a tad.