I'm going to translate my application strings.xml file. Which is default language of strings.xml file? because now i need to support italian (the language with i've write strings.xml for now) and english. Should i use string.xml for english and create
res/values-it/
folder for italian, and translate "default" strings.xml in english?
strings.xml is the default and will be used if there is no country specific file like res/values-it/strings.xml or res/values-fr/strings.xml. Read more about Localizing with Resources.
I would personally use strings.xml with english translations as a fallback as you already suggested.