Heck, Unicode is a mess already. But that's mostly because (a) language and scripts are messy, and (b) the original aim was to unify and encompass all existing character sets, and some of those were messy as well.
While there was considerable uproar over Emoji and there still often is over yet another fifteen symbols that everyone thinks no one would ever need or use, the bulk of the Unicode character set is still scripts for human languages. And some of those are only relevant for a very small minority, say, archaeologists. But that's fine. There's enough space, we're nowhere near to running out and Unicode enabled all sorts of cool things in computing that simply were not possible before or only with awful hacks and workarounds.
A text file, a webpage, or a database table can only contain textual data in a given encoding.
That's because every byte stored in the file, for example byte number 188, either means "¼" (as it does in ISO/IEC 8859-1, aka. Latin-1 or ANSI), or it means "ỳ" (as in ISO/IEC 8859-14) or "ｼ" (in JIS X 0201, one of the many Japanese encodings that were devised over the years.)
How do you know which encoding a certain file uses? In general YOU CAN'T and this was the source of many problems and "solutions" which caused even more problems over the years.
Well then, how did you mix symbols from different alphabets, say in a dictionary or in a post that talks about them, like this very post? YOU COULDN'T, short of doing ugly hacks and other subterfuges, like using GIFs for all foreign characters.
Unicode gave a distinct number (or "codepoint") to every character and symbol known to man (within reasonable limits) and this allowed a lot of things that we take for granted nowadays, including this very post, were I just copied and pasted various symbols from their Wikipedia pages and just expect it to work.
Fun fact: Japanese even has a word for foreign characters, "gaiji", and it's extremely common in Japanese ePUBs to use small square images very frequently for characters not in the current font, using the term "gaiji" in the CSS class names used for these characters. And at least one mainstream ePUB reader has special code to detect these gaiji and adjust its rendering to make them behave better.
Similarly, the word "loanword" (used to describe words borrowed from other languages) is gairaigo 外来語 which is literally 外来 (gairai) "foreign" + 語 (go) "word/language". Japanese is filled with words where you can often figure out the meaning purely from the characters used!
Conversion between different character codes became much easier. (Å (U+00C5) is canonically the same as Å (U+212B) but the latter exist only for round-trip compatibility.)
Unicode defines normalization algorithms (is é its own character, or e with a modifier character?).
I can have a document which combines English, Russian, Arabic, and Chinese, and expect it to be readable and editable by many different tools.
> I can have a document which combines English, Russian, Arabic, and Chinese
English combines with top-down Chinese, and English combines with right-to-left Arabic, but top-down Chinese and right-to-left Arabic don't combine properly in the same document using Unicode -- the Arabic will be written bottom-up instead of top-down when embedded in the top-down Chinese.
I meant something simpler, like: The word 'computer' in English is 计算者 [jì suàn zhě] in Chinese, Компьютер in Russian, and حاسوب in Arabic."
Try that without Unicode.
It's of course possible with TeX, and no doubt other solutions. Which is why I added "and expect it to be readable and editable by many different tools".
(As a real-world use case, look at Knuth's "The Art of Computer Programming" and see how he credits people using their full names, in their own written language.)
Do you know when you would use 计算着 over 电脑[dian nao]?
计算着 I guess more literally translates to "one who computes", whereas 电脑 translates to "electric brain" which is a way more fun image, but I have no idea how the usage varies.
I am not a native speaker and terrible at googling this, but I've once heard that 電腦 was originally the Taiwanese way of saying it and 計算機 the Chinese way, in the same way that 'program' is still called 程式 on one side of the strait and 程序 on the other, or 'internet' is either 網絡 or 網路. The names of movies and video games are also generally different (PRC, HK, TW).
计算着 [jisuanji] is the older usage that harkens back to the days when computers were mainframes and terminals and not in every household. Generally everyone says 电脑 [diannao] these days.
Someone I know worked at a company that sells a content management system with version control. Bigcos use it to keep and update lots of marketing materials and manuals. Those responsible for product x or area y can see what's been added by others, and update their own versions, and record that.
In this way, new FAQs and other updates spread to all the markets easily.
It's vastly easier to do this stuff when all the documents use the same text encoding. Even if noone can read everything, the fact that everything uses the same encoding means that any pair of languages you can read are technically readable.
While there was considerable uproar over Emoji and there still often is over yet another fifteen symbols that everyone thinks no one would ever need or use, the bulk of the Unicode character set is still scripts for human languages. And some of those are only relevant for a very small minority, say, archaeologists. But that's fine. There's enough space, we're nowhere near to running out and Unicode enabled all sorts of cool things in computing that simply were not possible before or only with awful hacks and workarounds.