What is the ruling on imitating disbelievers when they say "Oh God," meaning Christ, if you say it imitating them but intending Allah Almighty, and is this imitation considered disbelief?

The saying "Ya Allah" (O Allah) is a sublime supplication and remembrance. The fact that disbelievers might say it, intending Christ by it, does not prevent its use. Muslims say it, intending by it Allah, the One, the Unique.