In today's program, Bill mentioned the poem that Willem Mengelberg wrote into his score of Gustav Mahler's 5th Symphony Adagietto. Here's the complete text:

Wie ich dich liebe,
Du meine Sonne,
ich kann mit Worten Dir's nicht sagen
Nur meine Sehnsucht
kann ich Dir klagen
Und meine Liebe
Meine Wonne!

How I love you,
You, my sun,
I cannot find the words to tell you.
Only my longing
Can I lament to you,
And my love,
My delight!

On the lower margin, also in Mengelberg's writing, we read "If music is a language, then this is the proof. He [Mahler] tells her [Alma] in tones and sounds, in music."

Excerpted from Constantin Floros' Gustav Mahler- The Symphonies