Which Standchen? I believe there are two....

If it's the solo song ("Leise flehen meine lieder") that you're after, I seem to recall that the Schirmer edition of Schwanegesang gives words in English as an alternative to the German. With copyright in mind, I'm not sure I ought to fish out my old copy and type out the words for public airing online! - but I imagine you could find a (second-hand?) copy of the music easily eough. Schwanengesang is in volume I of the Schirmer edition of Schubert's sogs.

It's a long time since I've looked at the score, but I seem to recall that the English is a pretty clumsy paraphrase. I don't wish to pry, but is there any major reason why you couldn't tackle the German? Rellstab's poem fits the melody so splendidly.