It seems that there are times when this shirt would really come in handy. Although...the only time that comes to mind when I've had a complete language barrier was in Turkey, and I'm not sure the t-shirt has a sign for "Ok, it's fine if you don't have a direct bus to Antalya today, but could we get there by taking a bus to somewhere else, then transferring?" Fortunately, I was able to communicate this with diagrams in my notebook. (And it occurred to me later that the guy probably spoke German. Oops.)
Oh, wait, there was another 100% language barrier moment - once in Morocco I had to explain, "No, this is my father, so we'd like a room with two beds." (Most people in Morocco seemed to speak French, but not that lady.) Fortunately, sign language got the concept across.