Know English? Indeed, "modern" English same as Sheridan? Evidently Lorien had been on ("under") Z'ha'dum for multiple thousands of Earth years. Even the most recent previous Shadow War would have been approximately 1260 AD on Earth, and they didn't talk like Sheridan in 1260 even if Lorien had visited Earth at that time. And the best evidence is that Lorien had not left Z'ha'dum for some multiple of Shadow Wars, something like 1000 years apart.

Maybe Lorien was simply telepathic, although if that's the case, he seemed to waste a lot of time talking and listening, and in general interacting with people on a physical level.