The reason why you don't understand is because it's shortcomings are your baseline, while more experienced people's baseline was people spending tens of millions to get something that only worked for toy examples.
Yes, I can list plenty of cases where translation fails. For example not understanding that in a conversation about specialist topic X (eg Ruby programming, or the game of G) that seemingly common terms have specific meanings. But I can also use it on a random newspaper article in a different language and expect to understand the result. This was something that I did not expect to happen in my lifetime.
To me google translate seems like the perfect illustration of the shortcomings of this purely data driven approach...
Alpha go, on the other hand is a much much more elaborated algorithm ( from my very limited knowledge) and it does produce amazing results.