come on, use "language specific glyph substution" on the last resort font to show Irish last resort glyph if the language is Irish. I know OpenType have it. Does AAT support language specific features?
You are welcome to lobby Apple to commission such an enormous font. You have, I think, no idea how much work that would be.
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Michael Everson * * Everson Typography * * http://www.evertype.com

