First impressions matter. Your platform's default language will be the language that users will be greeted with when they first visit, so it's important to get it right!
To do so, go to Settings > General > Languages and make sure that in the Languages section your chosen default language is the first box on the left in the bar. If you want to change it, simply delete the other languages accordingly so that the language you want appears on the very left.
The language that the user registers their account in automatically becomes their “preferred” language, which specifies the language that the platform is displayed to them in and also impacts on how their ideas and comments are auto-translated, should you have the auto-translate function enabled on your platform.
A user can also change their preferred language anytime by going to their account settings, then scrolling down on their profile to the languages setting.
Do you have any questions or need help? Don't hesitate to send a message to firstname.lastname@example.org!