Why singers and pianists memorize music is beyond me. The answer is stimulus / response. Question / answer. Most of us are not fluent in foreign languages. There are times when I wonder if anyone is anymore. Good singing is like, what's your name, Marc Innes. No delay. No hesitation. No time delay. Natural. Honest. Believable. If one leads a catalyst to accomplish this, then one needs a catalyst. Rote repetition sounds incomplete. Unbelievable. Memorization or believing in what you are doing.
How can you act out your part if you don't know it by heart? Most singers are fluent in several languages. At least the working ones are. I know a number of Americans who sing in Europe and they are really good at the languages of the countries where they work. Ewa Podles wants her accompanist to play her music by heart. She does not want a page turner on stage either. That may be somewhat extreme, but I can see her point that she wants the accompanist, usually her daughter in law who teaches at Juilliard, to be completely comfortable with the music. I can't imagine working in Germany and not knowing at least some German before going over. Some Americans who work in American houses actually work in Italian because it is the language everyone in an Italian opera speaks. Maria