You must be logged in as an Administrator to change this setting!
When a new user is created they will be assigned whatever has been assigned as the default global language. When they login they will still be able to select their own preferred language - they will be prompted to change it during the first-run login wizard.
You can change the default so that subsequently created users will see a different language.
Steps
Navigate to the Global settings page.
Scroll down to the bottom of the page and locate User settings.
Click on Change and a drop-down menu will appear allowing you to change the language.
Click Save to complete.
This setting will take now effect for newly created users.