What evidence is there that Cyrillic is a single script?

Question

What linguistic evidence is there why the writing system used by Russian is considered to use the same script (Cyrillic) as the writing system used for Macedonian or Serbian (when written in Cyrillic letters)?

When Hungarian text refers to a foreign language proper name (such as the name of a person or town) that is written in the Latin script in its original language, the name is written as in the original language, even if this includes letters or accents that aren't used in Hungarian. Names written this way can get Hungarian grammatical suffixes, such as for noun declination. This is not only an academical rule, but is actual practice in news articles for general audience, when they mention names from eg. Slovakian, Croatian, French. This shows that those languages are written in the same script (Latin) as those other languages.

In contrast, proper names from foreign languages not written in the Latin script, such as from Russian, the name is transliterated to Hungarian based on its pronunciation. As a result, you never words written in the Russian alphabet with a grammatical suffix written in the Hungarian alphabet. This is because Russian is considered to be written in a different script.

Are there cases when a Russian text contains a Serbian or Macedonian name in its original spelling, containing letters that don't occur in Russian (such as ј or њ), but has Russian grammatical suffixes? Or is there other evidence that shows that the alphabets are mixed?

Obviously we can't start treating Cyrillic as two or more scripts now, the way Unicode has decided that Coptic is a separate script from Greek. It is too late for that because there is already a very large corpus of Russian, Macedonian, and Serbian text represented digitally. I am merely trying to understand why they were decided to be treated as a single script originally, and especially the linguistic (not political) reasons for this.

Answer 1

Consider the fact that Latin script is used to write French, Spanish, Portuguese, German, English, Norwegian, Saami (and the list goes on). No two of these languages use exactly the same letters. The meaning of "script" and the interpretation of modifiers like "Cyrillic", "Latin" has nothing to do with the structure of the languages being written, it has to do with identifying a historical "base" writing system (the letters used for writing Latin; the letters created by Cyril and Methodius; the letters for writing Ge'ez).

I think the question about sociolinguistic writing practices in Russia is a separate question. Most English-speakers modify non-English letters when they face <ø æ ß> in foreign words, yet many English-speakers preserve such letters. Sociolinguistic questions about usage patterns are never well-served by asking "What do speakers of X do", as though there were no distinctions made in the society.

Answer 2

Russian always re-writes foreign words in such a way so that the new spelling to reflect its pronounciation according the Russian reading rules not dependent on the language of origin. At most it can preserve some spelling exceptions where different variants of spelling lead to the same reading, such as starting a word with я- or йа-, ё- or йо-, where the both variants are read the same, but one is more often to be met in foreign words.

So, if a Bulgarian name is read differently than would a Russian speaker read looking at its original spelling (or contains non-Russian letters), it gets re-written.

Note that even Russian slang or contracted words are likely to be written according to their pronounciation rather than etymology.

Answer 3

Unicode does not have codes for all the letters of the Coptic alphabet, but only for the fourteen signs that do not occur in Greek as well. Thus, it treats Coptic in exactly the same way as the non-Russian forms of Cyrillic script.

Anyway, I think this question is not about linguistics, but about computer coding.