'Dreamcoat'; Jessye Norman; Jewish Traveling Theatre; Copley Sq. Ballet; Traveling Jewish Theatre

''Yiddish is the language of love songs and lullabies.'' So says one of the two characters in ''The Last Yiddish Poet (An Incantation Against Woe),'' by the San Francisco-based Traveling Jewish Theatre. It's both a celebration of life and a lament for the death of Yiddish culture and for Yiddish poets killed in various purges.

It's a swirl of Jewish vaudeville comedy (complete with fake noses), poetry, masques, music, and drama. Some of it works, some doesn't. The dialogue is by turns funny, self-depreciating, and poetic. And the two actors - tall, sticklike Corey Fischer and short, morose Albert Greenberg - bounce as well off each other as they do off the walls.

The piece lurches from humor to horror: At one point a harsh spotlight pins them in place; they back away, slowly removing their clothes. The terror of the Holocaust could not have been more effectively conveyed.

However, in spite of some fine moments, the piece has a frustrating lack of focus. And though the company aims to present ''a Jewish theater that is accessible and enriching to people of all backgrounds,'' there are enough unexplained Yiddish terms and cultural references to keep one feeling in the dark. It is, however, an admirable attempt to keep alive a vanishing tradition. At the Boston Shakespeare Company through July 1.