What the Unicode Character Keyboard does is add a widget to the Post and Page edit panels with a selectable collection of Unicode character sets as defined by the Unicode Consortium. This organization is a world-wide organization whose charter is to create specifications to define international character sets for all types of computing applications and situations. The widget displays a series of key images representing the contents of various character sets, and the character representations within the set can be clicked to send that character to the edit window.
The contents of this widget can be selected from a large number of defined character sets, ranging from several European and Eastern languages to a wide variety of dingbats, symbols, images and operators, even some oddities such as the Phaistos Disc and ancient Cuneiform characters and the Emoji pictographs (of which only the last of these are implemented at this time.) While large, the list of character sets included with this initial release is by no means a complete representation of the entire Unicode definition.