Now Off-Broadway, National Yiddish Theatre Folksbeine’s glorious production of “Fiddler on the Roof in Yiddish” breathes fresh life into a treasured property from the golden age of musical comedy, forcing audiences to interact anew with what is now one of the most well-known and performed musicals of all time, and providing, in return, a host of vital performances and resonant insights.  It is, in short, a revelation.  See it, or regret it.