Question: are Boulevard Solitude and Moses und Aron both German librettos?

Context paragraphs:
Der biblische Weg: Der biblische Weg ("The biblical Way") is a 1926 prose drama or play in three acts by Arnold Schoenberg.  The plot of the drama deals with political aspirations in a modern setting, the downfall of the chief protagonist comes about through his attempt to combine the principles of both Moses and Aaron.  Schoenberg used the play as an instrument of propaganda to promote the idea of a militant United Jewish Party.  Although the play shares a biblical source of inspiration with Schoenberg's opera "Moses und Aron", the play, a largely political work, has a very different focus from that of the opera, which is concerned chiefly with questions of theology and aesthetics.

Moses und Aron: Moses und Aron (English: "Moses and Aaron") is a three-act opera by Arnold Schoenberg with the third act unfinished.  The German libretto is by the composer after the Book of Exodus.  Hungarian composer Zoltán Kocsis completed the last act, with Schoenberg's heirs' permission, in 2010, but as of 2014 "Moses und Aron" was almost always performed as Schoenberg left it in 1932, with only two of the planned three acts completed.

Helmut Kretschmar: Helmut Kretschmar (born 3 February 1928) is a German classical tenor who spent most of his career performing in concerts and recitals with major orchestras and at important music festivals internationally.  Although he focused his career mainly within the concert repertoire, Kretschmar did appear two times on the opera stage, notably singing in the world premiere of Arnold Schoenberg's "Moses und Aron" in 1954.  Possessing a rich and warm lyric tenor voice, Kretschmar excelled in the concert repertoire of Johann Sebastian Bach, George Frideric Handel, Joseph Haydn, and Felix Mendelssohn.  Also an admired interpreter of Lieder, Kretschmar performed and recorded a number of works by Franz Schubert, Robert Schumann, and Hugo Wolf.

WDR Rundfunkchor Köln: The WDR Rundfunkchor Köln (West German Radio Choir Cologne) is the choir of the German broadcaster Westdeutscher Rundfunk (WDR), based in Cologne.  It was founded in 1947.  The choir premiered works by contemporary composers including Arnold Schoenberg's unfinished opera "Moses und Aron" in 1954, Karlheinz Stockhausen's "Momente", Luigi Nono's "Il canto sospeso", Bernd Alois Zimmermann's "Requiem für einen jungen Dichter" and Penderecki's "St Luke Passion".

NDR Chor: The NDR Chor (North German Radio Choir) is the choir of the German broadcaster Norddeutscher Rundfunk (NDR), based in Hamburg.  It was founded in 1946, with Max Thurn as the first director of then 55 singers.  The group has participated in premieres of contemporary music, such as the posthumous concert premiere of Schoenberg's opera "Moses und Aron".  It is also known for a capella music, introduced by Helmut Franz such as a recording of all such works by Johannes Brahms.  The current artistic director is Philipp Ahmann, who has held the position from 2008.  NDR Chor, now a group of 28 singers, is one of the leading professional chamber choirs in Germany.

Moses und Aron (film): Moses und Aron, known in English as Moses and Aaron, is a 1973 film by the French filmmaking duo of Jean-Marie Straub and Danièle Huillet based on the unfinished opera of the same title by Arnold Schoenberg.  During its 1975 run at US festivals, it was also known as "Aaron and Moses", and was frequently reviewed as such.

EuropaChorAkademie: The EuropaChorAkademie (European Choir Academy) is a German mixed choir, founded by Joshard Daus in 1997 as a group formed by students of two music universities, the University of Mainz and the University of the Arts Bremen.  They have performed internationally and recorded choral works including Mahler's Second Symphony and Schönberg's "Moses und Aron".

Boulevard Solitude: Boulevard Solitude is a "Lyrisches Drama " (lyric drama) or opera in one act by Hans Werner Henze to a German libretto by Grete Weil after the play by Walter Jockisch, in its turn a modern retelling of François Prévost's "Manon Lescaut".  The piece is a reworking of the Manon Lescaut story, already adapted operatically by Auber, Massenet and Puccini, and here relocated to Paris after the Second World War where, as is noted in Grove, the focus of the story moves away from Manon and towards Armand des Grieux.  It became Henze’s first fully-fledged opera.  The work stands out for its strong jazz influences, from a composer who had hitherto been associated with twelve tone technique.

Ursula Zollenkopf: Ursula Zollenkopf is a German classical contralto singer.  A member of the NDR Chor based in Hamburg, she appeared as a soloist in opera and concert, including premieres of contemporary music such as Stravinsky's "Threni" and Schoenberg's "Moses und Aron".

Hans Herbert Fiedler: Hans Herbert Fiedler (November 10, 1907 in Triest – February 14, 2004 in Munich) was a German operatic bass and actor.  He is best known today for portraying the role of Moses in the original 1954 production of Arnold Schoenberg's "Moses und Aron".

Supporting paragraphs: Boulevard Solitude Moses und Aron
Answer: yes