''Dalliance''''Undiscovered Country''''Rough Crossing''''On the Razzle''''The Seagull'' This fourth volume of Tom Stoppard's work for the stage brings together five of his most celebrated translations and adaptations of plays by Arthur Schnitzler (''Dalliance'' and ''Undiscovered Country''), Ferenc Molnar (''Rough Crossing,'' a classic farce set aboard an ocean liner), Johann Nestroy (''On the Razzle,'' a mad chase through Vienna), and Anton Chekhov (''The Seagull,'' the classic Russian country tale). According to ''The Times'' of London, ''Adaptation in Stoppard's terms means finding a sympathetic text and using it as a springboard for invention that leaves the original far behind.'' In adapting these plays--some classics, some nearly forgotten--for the modern stage, Tom Stoppard has added his own unique elements of dazzling wit and verbal brilliance, hilarious parody and cutting satire, to create works that stand as exceptional works of theater that do not belong to any one age.