Jibber jabber is [Incoherent] and [unintelligible] rapid speech often in [slang] or [patois]. Used in the UK as a [disparaging] name for other languages such as French, Spanish or American.
> “It was all jibber jabber. Couldn’t understand a dam’ word the wretched feller was sayin’, Jeeves.”
> “But, Milord, he was an American.”
> “Yes?”