In fact, it was the Austrian-born two-time Academy Award-winner who suggested the idea of including a 19th-Century German lullaby Washington would sing as a linguistics exercise in the film, which she revealed in an interview with Collider.
To play Broomhilda von Shaft, the enslaved wife of the title character in Django Unchained, Kerry Washington had to learn German for the first time, and cites her co-star Christoph Waltz as a great on-set tutor.
Seeing it as a perfect alternative to Quentin Tarantino’s original intention for the character to whistle (which the actress cannot do), Washington’s recording of the song became part of the finished product.