Change your UI language
If you want to change the language of your operating system follow these steps.
Open the Control Panel and click on the Add a language option under Clock, Language and Region section.
On the Change your language preferences page click on Add a language button.
Select your preferred language and click Add.
You cannot simply switch to any UI language only the most popular ones are available, for example German, Spanish, etc. So if you want to use and add an exotic one you need to check a display language is available.
To switch the language click on the Options, next to your selected and added one. On the next screen click on Download and install language pack.
This starts the download, and when finished installs it, like an update.
When the installations is finished and the new language is not your first in the list you need to override the display language. On Change your language preferences window click on advanced settings. Change the first section to your selected language – it should be in the list.
You have to log off for the changes to take effect.
Other accounts, welcome screen
Still, existing accounts and new user accounts won’t use the selected language, this only affects yours. To manage these and the welcome screen, click on Apply language settings to the welcome screen, system accounts, and new user accounts option on the Advanced settings panel.
On the new dialog panel click Copy Settings button
Review your settings for display language, keyboard layout, format and location (Current user) then select welcome screen and/or new user accounts to replace their settings with your new ones, click OK.
For now it’s obvious that this is a per user setting. So your children can use French interface to practice the language while you still use it in English.