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1.
The belief that, when high, you can speak two or more languages

Can be actual knowledge of the language that was forgotten but was remembered because your high. Or a completely false belief (when their translation has nothing to do with the actual translation)
A "Como estas"
B "Bien y tu?"
A "You speak spanish?!"
B "I do when im high"
A "Ah, so your highlingual"

OR

A "Como estas"
B "Si mucho por favor'
A "What?.."
B "I said im high too. You must not know that im highlingual'
by Jay and Day May 18, 2013
 
2.
When you are so high that you might as well be speaking another language because no one can understand you.
Jared: Dude what the hell is Alec talking about?
Mike: IDK, he's speaking gibberish right now.
Jared: Yeah he is definitely highlingual.
by GrizzGreezy July 17, 2011