Water level allows you to scale the watering time based on the percentage. It can be used by the weather based adjustments to reduce or increase watering based on the weather or also manually adjusted.
The localization is in fact there for Italian as I have verified this. Could you force restart the app and check if it fixes the issue?
I have updated the localization text today from GetLocalization as new languages have been added and other translations updated. I will try to push this app update ASAP.