Plural form of Libretto is Libretti.
Libretto is the singular. Libretti is the plural. Sometimes librettos is also commonly used as the plural.
Librettos
librettos
Liberetti
Libretto (singular) or Libretti (plural)
A libretto is the text a composer sets to music. It contains all the dialogue and stage directions of the play, and can be dramatic or comedic. Libretti (Italian plural for Libretto) without the music would simply be scripts.
Libretto is the text to an Opera.
Libretto.
There is no plural form. Do and Do not are verbs
The plural form of him, her, or it is them. (objective pronouns)
Bridges is the plural form of bridge.