Tracking your theme

How do theme creators know where the theme they developed is being used?

It would be great to gain data on what language a theme is being used in, reasons for uninstallation etc. It can help improve the theme – without collecting user data.

Is there a method to implement in the theme code, or is that wrong? Would it be through customer support? Or voluntary submission?

How would you go about finding out where your customers are using your theme so that you can improve it by seeing real-world use cases? While still respecting privacy.