We normally use past simple tense to talk about the past and past perfect tense to talk about the past in the past, i.e. to talk about some event that that happened before some other event. I often see that when we use past perfect tense, we use it with past simple tense,e.g. I had learned Chinese before I moved to China. What if I use a non-finite adverb clause, e.g. I had learned Chinese before moving to China? How different are these two alternatives?