The echo isnt really used for the beast tribes as it may appear. While I cant speak for the majority of the "bad" beastmen, it has been shown on numerous occasions that most of the beast tribes understand the Eorzean language. This is shown when duringnthe beast tribe quests, barring Sahagin maybe, where each tribe communicates with several other NPC. Additionally the Black Mage quests has you communicating with several beastmen as well, though the dialogue indicates that the other NPCs involved have all communicated together. So the beastmen can speak the "common" tongue.