He wouldn't even recognize this "mass".
“He wouldn’t even recognize this “mass”.”
Actually, he would recognize it as much as he did the old Mass the first time he saw that - in other words, not at all, but then he would dutifully learn it. Speaking only the language of the Oglala Lakota (Sioux) originally, he had to learn the Latin responses and eventually could sing the whole Latin Mass. https://books.google.com/books?id=uBHUzKnb7M8C&pg=PA68&lpg=PA68&dq=black+elk+latin&source=bl&ots=vStlQb9c3L&sig=E9kI6nEKpUhXpWcaStlQA0Cpc1Q&hl=en&sa=X&ved=0ahUKEwi-gtO1vLHXAhUX2GMKHaLJBSgQ6AEIQzAE#v=onepage&q=black%20elk%20latin&f=false
Since he wanted his children to learn English (see the same link above) he would probably have welcomed a Mass in English to some degree.