How to create a new language for Samsung keyboard?

Question

Android

Here such a thing, in general, for some reason I needed to create a new pack of some new language for the "Samsung Keyboard" (For the standard keyboard - an application that is already installed on all models of Korean smartphones). Or at least add some new characters to the Russian keyboard, for example, something like: when you double-click a number, this character appears: "ü".
I tried to download a separate application for Android, in principle I managed to add these few characters, but in the end I got a boring keyboard with fewer options and functions, relative to the standard Samsung keyboard, of course. Yes, and from the point of view of design, it turned out crooked.
Please help me in this mission.