On a fresh install, only en_US and fr_FR sounds are installed. Canadian French and German are available too.
To install Canadian French sounds you have to execute the following command:
apt-get install asterisk-sounds-wav-fr-ca wazo-sounds-fr-ca
To install German sounds you have to execute the following command:
apt-get install asterisk-sounds-wav-de-de wazo-sounds-de-de
Now you may select the newly installed language for your users.
Asterisk will read natively WAV files encoded in wav 8kHz, 16 bits, mono.
The following command will return the encoding format of the <file>
$ file <file> RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, mono 8000 Hz
The following command will re-encode the <input file> with the correct parameters for asterisk and write into the <output file>:
sox <input file> -b 16 -c 1 -t wav <output file> rate -I 8000