Basically, a character knows a language... except that their knowledge of said language is basically "really cheap traveller's phrasebook made by asshole who hates people". Or they're actually usin' one.
Example, you're a human that knows "mangled" Siik'Maas. A Tajaran engineer attempts ta tell you something in Siik'Maas. What they say:
"The supermatter is going to explode!"
What you hear could range from:
"Meow yowlmatpurr is mrowlng emrrrrrrr!"
ta
"I want chicken I want liver!"
Confused/amused/incensed, ya consult yer memory/book and attempt ta reply in their language. What the Tajaran hears could range anywhere from:
"Fhat sis mau ray?"
ta
"Please direct me to district of loose moral females."
Codewise, this could be somethin' that could randomly replace/add/drop random sequences of letters, words, or even choose from a list of hilarious phrases. Imagine the delicious miscommunication that could result from this.
EDIT: Gameplay and/or lore-wise, this could also be used ta limit people who shouldn't be actually able ta speak a language, say, a tajaran tryin' ta whistle robo-speak.