Did you read TFA? His name matches [A-Za-z]+.

Maybe he meant "can also cause problems in old systems"

This mindset causes trouble. Machines and programs must adopt to reality. Not vice versa.

Causes trouble for simply poor programmers or poor systems.

Have you heard about Unicode and non-Latin alphabets?

GDSes run on mainframes with roots in the 1970s, they predate unicode by 20 years.

If that means that they can no longer represent reality, then that's a bug. "We've gone 50 years without actually updating our systems to fix problems" is a less-than-impressive response.

Which is what this whole discussion is about. As well as understanding the root cause of such bugs (in-band signaling, etc), to start to fix them ideally.