I occasionally have conversations with people about the Traditional Latin Mass and almost invariably they express the point that no one understands the Latin so they aren't really getting anything out of it. If that were true, it might be a good argument for the vernacular. Although I wonder why, in that case, the committee that developed the Novus Ordo didn't just translate the Mass into English. But that's a thought for another day.
Whenever someone tells me that people didn't understand the Mass that was the norm for centuries, I ask myself whether that was really true. Do we only understand the spoken word? And, in fact, does the spoken word sometimes fail to impart a message? My contention is that the answer to those questions is NO and then YES.