noun
Colloquial and slightly playful term for a foreign language, often used when the speaker does not understand it or finds it exotic.
彼が話しているのはあちら語で、私にはさっぱりわからない。
What he's speaking is a foreign language, and I can't understand it at all.
Compound of あちら (that direction, over there) and 語 (language). The exact derivation is uncertain, but it likely arose as a colloquial way to refer to a language from 'over there' (i.e., abroad).