I would like to create a new “International Text Input Source” along the lines of the built-in Japanese input source where you can type in roman letters and get a drop-down of choices to choose from. However, I have no idea where to start work on such a thing. Is it feasible, or would it be a complete hack?
All I’ve found so far is the Text Input Source Services which seems to be all about dealing with existing input sources.
Any pointers on where to begin would be highly appreciated, thanks.
Sounds like what you are really looking for is documentation the Input Method Kit (which was introduced with Leopard).
Here’s Apple’s release note and a reference guide.
The reason I thought of this answer was because I had worked with Apple’s Number Input sample code a year or two ago.