I hadn't known that point about sort order. Wait, so suppose a language that uses the same alphabet as English used a reversed alphabet ordering. Would unicode include z-a somewhere else to support that language?
Probably, yeah. If it's got a fundamentally-different collation, then it's not the same script as the Latin alphabet per se.
However, due to how annoying it is to deal with languages with the same glyphs but a different order ("I don't know where to find things in this translation dictionary!"), languages that share a set of glyphs have tended — ever since democratized access to printing, and dictionaries to create "canonical" orderings — to gravitate toward a shared ordering for the common-denominator subsets of their alphabets.
German, for example, has an alphabet that's like the Latin alphabet but with some "extra" letters — but, however they did it way back when, the German alphabet today "embeds" the Latin alphabet in Latin order at the beginning, and then puts all the extra letters at the end. So German doesn't need another set of Unicode code-points for A-Z; it just needs codepoints for those extra letters.
>So German doesn't need another set of Unicode code-points for A-Z; it just needs codepoints for those extra letters.
The extra letters would sort differently though right? I wouldn't expect ö/ä/ü to sort after z. For ß I guess it's not a concern since it never appears at the start of words.
No, that's not a relevant concern. In the same way, Unicode sees no problem with assigning LATIN CAPITAL LETTER I (U+0049) and LATIN SMALL LETTER I (U+0069) to the glyphs of the Turkish alphabet that have those appearances, despite the fact that in Turkish they are two different letters. (And therefore capitalization has to be done by an algorithm that is aware of what language you want to do capitalization in.)
By contrast, GREEK CAPITAL LETTER A is U+0391, separate from LATIN CAPITAL LETTER A. There is no principled reason for this.