(Credit: Monika Ritterhaus) “Die lustigen Weiber von Windsor,” like the vast majority of Singspiele, is not well-known outside the German-speaking world. Even in its native Germany, it’s mounted infrequently. Its story, however, is almost universally known. Like Verdi’s “Falstaff,” it’s closely based on Shakespeare’s “Merry Wives of Windsor.” A few details are Germanized: Alice Ford becomes Frau Fluth, and her {…}