在SettingsActivity中更改应用内的区域设置（语言）

I want that the user is able to change the app language (strings are in folders like strings-de/strings.xml or strings-zh/strings.xml). It works fine when i change the phone settings to chinese or whatever, but what I am trying to do is the following: I have a MainActivity with a few fragments, and in my actionbar i have a settings icon, when the user clicks it, a settingsActivity opens, and i have a menu item where the user can choose his preferred language. When the user clicks it, the app should reload and use my strings from the selected language. How can i achieve this? and in which activity does the code belong? thank you in advance.I want that the user is able to change the app