It is an enormous effort (read investment) to get to a point of detail, where such a library becomes usable to a wide audience.
Consider a simple text input: In some languages (e.g. 'syllable based' korean Hangul) you have to compose multiple keystrokes to get to a complex letter. While you type, the last and as well as the second-to-last complex-characters might still 'trade' consonants and vowels among each other.
Now layer in more Dimensions, such as validating that input or line-wrapping, elision and many more.
To my mind, only few libraries got to this level of detail without breaking apart on complexity. It requires high maintainer stamina or massive investments.
Most of your input example is nowadays typically handled by code outside the GUI toolkits themselves (such as the IME, the text shaping and the font stack), although the general "the GUI devil is in the details" thrust is right.
Consider a simple text input: In some languages (e.g. 'syllable based' korean Hangul) you have to compose multiple keystrokes to get to a complex letter. While you type, the last and as well as the second-to-last complex-characters might still 'trade' consonants and vowels among each other.
Now layer in more Dimensions, such as validating that input or line-wrapping, elision and many more.
To my mind, only few libraries got to this level of detail without breaking apart on complexity. It requires high maintainer stamina or massive investments.