“We speak a pure English, not mixed in with all kinds of Yeshivishe and Yiddish words.”
I heard a story about one Rosh Yeshiva at YU. A talmid asked a question during shiur in heavy Yeshivish. The RY asked him to restate the question in his choice of language: English, Yiddish, or Hebrew were all acceptable. The point is that we should use proper grammar and vocabulary in whatever language we use.