A SurfaceGui that asks you to select a language before you continue. A bit like CheckMeIn.
How do I save that data? How do I ask different players?
Doing it in a LocalScript but I don’t know how to store that information.
Thanks for reading 
Why don’t you just use the Roblox localization feature? That automatically pairs the language the player has used to the game. Many top games use this system like Jailbreak, Meep City, ETC.
Roblox has a localization service which does the job automatically without the need of guis or localscripts, I suggest using that as it’s very good and Improved at the moment!
Evidently, you haven’t searched this up or aren’t willing to do some testing in Studio. A few seconds of my time gave me the answer I needed plus a code sample.
LocalizationService.GetTranslatorForLocaleAsync.
It is absolutely important that you search these things up first and test before you post threads to this category. There are questions you can easily answer for yourself if you spend time and effort to actually get to the end result you’ll be looking for, rather than waiting for someone to freely hand answers out.
To memorise and get the answers handed to you is one thing; but to actually understand what you’re doing is invaluable.