You can change the game's language by following these steps:
2) Select "Settings" 
3) Tap on "Language" 
4) Select the desired language and then tap "Confirm"
When you switch languages, your level will stay the same and will change at the beginning of the next level.
The Daily Challenge is currently only available in English. You can still access the challenge with the game set to Spanish, however, the words will be in English.