the audio streams/A1_Audio contains these items in EU:

EN: English
ES: Spanish
FR: French
IT: Italian

Global: Ambient sounds

a file by file breakdown of en/global can be found in AudioMap.yaml
the es,fr,it folders contain the same files as en

the language folders contain .exa.snu audio files, each represent a charactors voice lines


the nature,contents,purpose of the mus files are unknown, but they are likely music tracks used in the game.
80b_mus.mus
bin.mus
brt_mus.mus
bsh_mus.mus
cheater.mus
gts_mus.mus
hub_mus.mus
loc_mus.mus
menu_mus.mus
mob_mus.mus
moh_mus.mus
mtp_mus.mus
nvq_mus.mus
rwc_mus.mus
spr_mus.mus
sss_mus.mus
treetemp.mus


the US version only has the EN and Global folders, and mus files

the EN and Global folders are actually created by me, normally the contents of those two folders would be in the root of the audio streams/A1_Audio directory, but I moved them to separate folders for better organization.