Say what you want but for modern UI localization and accessibility are part of minimum feature set. Those two massively increase complexity (UTF8, IME, Braile, Text to speech, etc.)
The big issue I'm talking about is cross OS UI Toolkit. Great your UI supports IME on Windows and Mac. Now do that for Linux, BSD, etc.
First they have to decide what distribution actually matters for the desktop, out of hundreds that get forked for frivolous reasons.
And yes accessibility and localisation were already a thing in Windows 3.x, classical Mac OS, OS/2,...