A system I worked on years ago was delivered in 4 languages. The app would (initially) guess your language based upon your browser settings.

As the translations were often in a state of flux we had a development version that was in swedish chef (bork bork, etc). This was never put into prod. It mostly helped us work on functionality without getting caught up in the actual text (lorem ipsum style).

However, down the line we got a batch of testers that were using our development infrastructure. Go figure, one of them has swedish as their browser preference... When they got "bork bork bork" they weren't impressed to say the least. Took us ages to convince them that it wasn't deliberate.