When Jesus said, "On this rock I will build my church," he was referring to Peter which in Greek means rock. Does this mean that Jesus could speak Greek? It's a long way from Aramaic!
Those of us who can speak another language know that you can only make a pun on words if you are fluent on that language. It is unlikely that Jesus knew enough Greek to be able to do that. The Jesus of history may have had a rudimentary knowledge of Greek so as to engage in general conversation, similar to what an European American would have of Spanish, but he was certainly not fluent. So probably this is the work of Matthew, who adds to Mark’s version of the incident the mention of the church, which was one of his special themes, but not of Mark or Luke, who never use the word in their gospels (cf. Matthew 16:13-23; Mark 8:27-33; Luke 9:18-20; see also Matthew 18:5-21). But Luke uses it in Acts because that was one of his main concern in that work, namely, to narrate the development of the early church.
Jesus spoke Aramaic. The play on words in Greek -- "petra" = rock; "Petros" = rendered "Peter" -- picks up on the word play in Aramaic ('kepha").