XEmacs had things (multiple terminals attached at once, internationalization, color themes, input methods, and so on) long before (like a decade before) GNU Ema

XEmacs had things (multiple terminals attached at once, internationalization, color themes, input methods, and so on) long before (like a decade before) GNU Emacs had them. But now GNU Emacs has them, so the only people still using XEmacs are approximately the people who got set up on it 20 years ago and don't feel like changing. It still exists because things don't pop out of existence when their main reasons for having been created long ago go away.