This guide will explain how to install a new language on the device and how to set it as default language (the screenshots are made using an Italian language device and add English language as default).
Write Filter to disable
To make the changes permanent remind to disable the write filter. See more on Using the Write Filter (Agile chapter) chapter.
First of all login the device with "Admin" user.
From Start menu click on "Settings".
From the "Settings" window click on "Time and Language".
Click on "Region and Language" tab, then click on "Add a language".
On the list of available language search for the desired language and click it.
Now that the language is installed click on "Set as default" to set it a the system language.
This will change only parts of the interfaces in the desired language.
To apply the language to all the system and user interface you have to open the standard "Control Panel" and click on the "Region" icon.
Select the "Administrative" tab and then click on "Change System Locale...".
From the combo box select the desired language and click "OK".
From the previous windows click on "Copy Settings..." and then flag the two options "Welcome screen and system accounts" and "New user accounts". Click "OK" on this window and click "OK" on the previous window to save the configuration.
The systems asks to reboot the device, click to reboot it.
Write Filter to enable
After this operation remind to enable the write filter to protect the device. See more on Using the Write Filter (Agile chapter) chapter.