speak so i can hear you
When they were twelve, Brittany watched a fascinating documentary about language games and immediately decided she and Santana needed one of their own. After a great deal of pestering Santana grudgingly did some research and they both sat down one long sleepover weekend to make their secret language.
After a few weeks and some weird looks from her parents, Santana stopped practicing the strange words, even in private. Brittany continued off and on for almost two months, despite the looks from her peers and irritation from her teachers (although neither from her parents).
But eventually some of the novelty wore off and Brittany went back to speaking english (mostly). A few more months went by and Santana had almost forgotten about their secret language.
Then their frustrated english teacher snapped and unleashed an angry tirade on an unsuspecting Brittany. Afterwards, devistated, Brittany entirely refused to speak english.
For six days Santana dredged up every half forgotten syllable to act as translator at school and home, while she and both their families tried to convince Brittany that the teacher was an asshole and it wasn't Brittany's fault and no she was not dumb, don't even think that!
On the seventh day, Brittany woke up and asked her parents what was for breakfast in words they actually understood. Everyone breathed a sigh of relief.