Can I change the Apple Watch simulator language?
Most certainly not possible neither via Watch Simulator UI nor iOS Simulator Watch app, but you can copy over values from iOS Simulator folder located in:
to the same file in your Watch Simulator.
Plist keys to look for:
You cannot change the Apple Watch simulator locale, but you can change the locale of your Watch App. I use this to test localization. To change your app locale, go edit the Watch App Scheme: Run->Options->Application Language - choose the language and re-run your Apple watch app.
Unfortunately it works only on Xcode 7.2, not on Xcode 7.1. There is no other known possibility.
There is a brand new library for language and locale automate testing. It's called
AutoMate. The documentation can be found here.