Title: ARIAS-PAZ. Motocicletas.
Author: Manuel Arias-Paz Guitián.
Publisher: CIE DOSSAT 2000.
Language: Spanish.
It is the most complete book on the mechanics of motorcycles which is in Spanish.
It touches on practically all themes even though some, such as the electronic injection are slightly overlooked.
To resolve specific doubts on any concrete model, the work shop manuals from the HAYNES or CLYMER editorial are a good option.