First of all, I completely agree with OP that "Dorset Perception still sounds fresh" after 20+ years. Legitimate creative geniuses. Dorset Perception is an absolute fucking classic.
The original lyrics are definitely Portuguese, although could definitely be part of a Portuguese/Spanish hybrid language, depending on one's lingual background. My best guess:
Portuguese:
Desafina
Canto mi amor
Tu és fixe, és muito bom (x3)
Tu és fixe, és mi amor
English:
Out-of-Tune
I sing my love
You are cool / great, (you) are very good (x3)
You are cool / great, (you) are my love
Also my best guess: this is probably a reference to glossolalia, the phenomenon of [apparently] speaking in an unknown language, especially in religious worship or during a psychedelic experience. "Speaking in tongues," in other words.
Trip like I do! Cheers!