My read has generally been that the Mamool Ja we've seen are speaking in broken Eorzean. The Echo can translate languages (evidently both ways, or else we'd have been pretty screwed for half of Stormblood), but it can't do much to clean things up when they aren't speaking clearly in the first place. Over in Tural the Mamool Ja will be speaking their mother tongue, so it'll be fine.

Alternatively, maybe that's just the Mamool Ja's thing, like how the sylphs struggle with names and first-person pronouns. Perhaps the Mamool Ja are perfectly intelligent, but don't feel the need to express that via complex language. If one or two words will get your point across perfectly fine, why structure a whole sentence around it?