And yes... they do speak Squid.
Nintendo of Japan just posted a behind-the-scenes video of the recording for the Splatoon’s soundtrack. Amongst the bands featured we have:
Squid Squad performing “Splatfest” which is also acts as the main theme for the game, the Squid Sisters performing their splatfest battle song “Paint it Your Color”, and last but not least the Chirpy Chirps perfoming “Quick Start” (some people know it as “You and Me”).
Sadly we didn’t get to meet Hightide Era, the secret identity of Totakeke will remain a mystery.