alt Hacker NewsFrom a German user perspective, ICU and your fancy library are incorrect, actually. Mass is not a different casing of Maß, they are different characters. Google likely changed this because it didn't do what users wanted.
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It isn't until it is, how would you write it when ß isn't available on the keyboard?
Which is why we also have to deal with the ue, ae, oe kind of trick, also known as Ersatzschreibweise.
Then German language users from de-CH region, consider Mass the correct way.
Yeah, localization and internalization is a mess to get right.
I never understood why the recommended replacement for ß is ss. It is a ligature of sz (similar to & being a ligature of et) and is even pronounced ess-zet. The only logical replacement would have been sz, and it would have avoided the clash of Masse (mass) and Maße (measurements). Then again, it only affects whether the vowel before it is pronounced short or long, and there are better ways to encode that in written language in the first place.
MASS is allowed casing of Maß, but not the preferred casing: https://www.rechtschreibrat.com/DOX/RfdR_Amtliches-Regelwerk... Page 48
The confusion likely stems from the relatively new introduction of the capitalized ẞ https://de.wikipedia.org/wiki/Gro%C3%9Fes_%C3%9F
Maß capitalized (used to be) MASS.
Funnily enough, Mass means one liter beer (think Oktoberfest).
Ah, let's have a long discussion of this.
Unicode avoids "different" and "same", https://www.unicode.org/reports/tr15/ uses phrases like compatibility equivalence.
The whole thing is complicated, because it actually is complicated in the real world. You can spell the name of Gießen "Giessen" and most Germans consider it correct even if not ideal, but spelling Massachusetts "Maßachusetts" is plainly wrong in German text. The relationship between ß and ss isn't symmetric. Unicode captures that complexity, when you get into the fine details.