At the current point in time there is no way to change your language from within Jetpack Joyride.
The game automatically mirrors whichever language is active on your device, unless your language is not supported in which case it should revert to English.
We are hoping to change this system in a future update and will post more information as soon as it becomes available.
In the meantime, changing your language at the device level should do the trick.
How do I change language
Last Updated: 454d