One can include all the Unicode characters. But is there a keypad that one can also use for copy and paste into whatever program you’re using? You’d specify the range for standard Unicode, and it would present what should be there, by the standard. And then you just press the button you want for a character with squiggly a over it and squiggly b below.
Babel Map is pretty good for cut and paste of any Unicode character.
For typing in Unicode, Opera Browser can be customized to type any Unicode character:
a ctrl shift = Insert, “Ā”
To type Ā with control + shift + A for example. āīūĀĪŪ