The sound files can be customized according to the special request, usually the sound file format can be MP3 or WAV. 

Any language or message is welcome. 
The message or file can be edited to the detail visible artwork to printing out, meanwhile add some more pictures to attractive the children.

And the papaer material should be art paper with hard cover, besides to support the sound module to mount on the book. 
The button sound module will glued on bottom side, and assemble with the books together.