German.

Studies by Bertini, Burgmuller, Czerny, Duvernoy, Gretchaninoff, Gurlitt, Heller, Kirchner, Lemoine, Schumann, Schoenmehl and others, arranged in order of progressive difficulty. These studies are fun as well as musically interesting and valuable.
The volume could be introduced in combination with vol. 3 of the piano tutor Piano Kids and subsequently be used in conjuction with other teaching material [e.g. Piano Kids in Concert, ED 8440).