I'm curious, how popular is the bible in Taiwan? And why does it use Taiwanese characters not commonly used elsewhere?
This Bible is not written in Mandarin, but rather Hokkien/Min (I suppose it's more correct to say "Southern Min," but I'm used to saying Hokkien and you'll see Taiwanese Hokkien as a term appear). And this is actually a kind of interesting statement about the written language. If you've ever talked about languages/dialects in the Chinese language family you might have heard something like "They might sound different but they all share the same underlying written language and are hence dialects" or the opposite "They're entirely separate languages akin to the Romance languages with their own spoken and written languages that might occasionally be similar/have cognates across different languages."
The situation is a bit muddier than either of those statements might suggest. As this example demonstrates, it's certainly NOT true that if you just wrote down any language/dialect in the Chinese language family it's intelligible to a Mandarin speaker. Chinese Unicode caters towards Mandarin and as you can see there's certain characters here that essentially never show up in Mandarin (and hence a Mandarin speaker might not recognize them). There are also characters that a Mandarin speaker might recognize but not understand its meaning in this case (e.g. some of the pronouns for example the third-person pronoun 伊 which is normally 他/她/它 or 其 in standard Mandarin depending on how formal the setting is). And certainly any Mandarin speaker can attest to the fact that there are certain languages/dialects that are not verbally mutually intelligible.
However, there often exists a written "embedding" of Mandarin into these dialects/languages that doesn't really have an analog among e.g. the Romance languages. For example, Cantonese pop music is often written in Mandarin, but sung in Cantonese, which means that each Mandarin character has a proper Cantonese pronunciation. It comes off as "Mandanrinized" and it's not the way people normally speak, but there's a standard, well-defined way of doing this, and it's intelligible (well at least in certain settings; if you speak like that normally you're going to have a problem). There isn't really a similar way of doing this for French and Spanish. You can't just take a Spanish work, pronounce it using a French pronunciation, and then voila have a French work. It's not even entirely clear for all words what "pronouncing it with a French pronunciation" means.
Nonetheless it's not the same thing as having a shared written language. Standard written Cantonese is going to be tricky for a Mandarin reader to read, just as this Hokkien Bible is going to be tricky for a Mandarin reader to read. And even this "embedding" I'm talking about isn't perfect since there are some Chinese characters that show up commonly in Mandarin but rarely in, say, Hokkien and vice versa. Having a shared set of characters only gets you so far when they can have somewhat divergent meanings and very divergent pronunciations. And it's not even the case that all dialects/languages have standardized written forms.
Regardless, despite the fact that there are many named languages/dialects in the Chinese language family, the mutual intelligibility situation isn't quite as fragmented as it's occasionally made out to be. There's a handful of large families that share a pretty high degree of mutual intelligibility among dialects/languages within them. A few examples are the Mandarin family of dialects (of which Standard Mandarin is a member), which probably has the broadest geographical distribution, running mainly in a diagonal from the Southwest of China (Sichuan) up to the Northeast (HeilongJiang), the Cantonese family of dialects, the Wu family of dialects, and the Min family of dialects.
Returning to this Bible, the funny thing here is that the preface to this Bible is written in Mandarin, but the Bible itself is written in Hokkien (which hints at some of the weird interconnectedness among Chinese dialects/languages). In turn the Chinese characters here are a transliteration of a previous Romanization of an Amoy (Xiamenese Min) translation of the Bible.
This post ended up running away from me a bit, so just to recap the original Unicode answer: Chinese Unicode caters towards characters that show up in written Mandarin and this isn't written Mandarin.
I guess this is similar to how every written english word has a well defined spanish pronounciation as if it were written spanish. You wouldn't always get something intelligeble from an english listener's point of view, but by the rules of spanish pronounciation, many english words have similar pronounciation when read as spanish. I don't think I've ever heard a song do something like you described between these 2 languages, though, and I'm not sure how it could be made to sound good either.
The Spanish-English example you give really only is a result of Spanish's regular correspondence between spelling and pronunciation (as far as my limited Spanish knowledge allows me to understand), that allows you to unambiguously pronounce most combinations of Latin letters. For example, there's a "Spanish pronunciation" of the Quecha written Latin script, but it's basically an unintelligible mess of sounds that violates a lot of Spanish sound rules. If you use some conventions to group letters together and settle on a single pronunciation of each of those groupings, you can do the same in English with any Latin letter combinations as well.
Generally speaking, pronouncing written English as Spanish results in something that neither Spanish speakers nor English speakers understand nor accept as part of their language. While there is a subset of vocabulary (most notably -ion words) that shares the same or similar spelling between the two languages, there isn't really a cohesive subset of the written language (that is imagine writing entire sentences and paragraphs) that can be shared.
Like you said, that's not really doable for spanish-english. There's words like "similar" which are written and pronounced the same in both languages, but there's not enough to write sentences.
FWIW it's not just songs; standard Mandarin is usually the prestige dialect/language so anything that's perceived as being more "prestige" than an everyday conversation (e.g. things that are meant to be formal or official or whatever) tends to become Mandarinized among the different dialects/languages. Cantonese is a special example because of Hong Kong's own interesting social environment.
For most other dialects/languages in the PRC, speakers just switch directly to Mandarin where they might have used a "Mandarinized" part of the dialect/language. Hong Kong is one of the few places where Mandarin comprehension is still not near-universal and so instead of just having Mandarin pop songs, you end up with Mandarinized Cantonese pop songs.
在呼召我之處 The Place Of Calling (國語+台語) - 約書亞樂團 Joshuaband https://www.youtube.com/watch?v=31q8w6JpndA
On the topic of cultural crossover, I can also recommend inner Mongolian folk metal (traditional throat singing mixed with electric guitars is brilliant - 九大圣器 Nine Treasures, 杭盖乐队 Hanggai). For Taiwanese, check out 滅火器 Fire EX., 一步 One Step, 閃靈 ChthoniC).
Maybe Bokmål is similar in this regard? The Wikipedia page says it's "Norwegianized variety of Danish": https://en.wikipedia.org/wiki/Bokmål
The whole story of how the various Scandinavian languages developed is actually quite interesting and has a lot of similarities to the situation among the different languages/dialects of Chinese. In particular similar questions of mutually intelligibility come up.
However, as I understand it, Bokmål in this particular case is not quite the same. It historically came from Danish, but now is a written standard for Norwegian that competes with Nynorsk (which is in itself a fascinating phenomenon; not many other languages have competing written standards). It's not really a current embedding of Danish into Norwegian so much as it is a written standard for Norwegian that historically developed from Danish.
I don't think that's quite correct. It is true that many older Cantonese pop songs were not written in Cantonese, but they were not written in Mandarin either; instead they were in what's called Written Vernacular Chinese (白話文)[1], which is based on a subset of Mandarin.
As an example of the top of my head, 咱們 is a very common word in spoken Mandarin, but it is never used in formal documents (written vernacular), and a Cantonese only speaker would have trouble pronouncing it.
[1] https://en.m.wikipedia.org/wiki/Written_vernacular_Chinese
Maybe I've lost touch with the current Canto-pop scene, but I seem to recall quite a lot of modern-ish Canto-pop (late 2000s) being written in Mandarin.
白话文 is sort of ill-defined. It really just means "vernacular written language" as opposed to Classical Chinese (文言文). There is a Yue vernacular (粤语白话文), Wu vernacular (吴语白话文), etc. There is also a Mandarin vernacular (which is what 白话文 usually refers to by itself in Mandarin) that you can further specify as 官话白话文 (although that term is getting quite specialized and not every native speaker is necessarily going to have heard of that), but that is exactly what it sounds like, the semi-formal written Mandarin vernacular. This is exactly the same situation as standard written English. While this is a restriction of "English" in some sense (does this include regional-specific terms such as "yous?"), it still is more or less equivalent to what most people think of when they think of "English."
咱们 is common in Northern dialects of Mandarin, but used to be a pretty strong marker for a Northern Chinese speaker. That's changed somewhat over time due to broadcast media and the primacy of some Northern Chinese accents, but you're still not going to hear a ton of older Southern Chinese speakers use 咱们 when speaking Mandarin (and when I mean south I mean essentially anyone from Jiangsu/Zhejiang on down) even if they speak pitch-perfect Standard Mandarin. They almost exclusively use 我们 instead (which is also valid Standard Mandarin, everywhere you would use 咱们 you could also use 我们 although not vice versa).
I think this is the phenomenon you're picking up on, that a lot of Northern Chinese Mandarin terms don't show up in Southern Chinese Mandarin.
More broadly, I think what you're pointing out is that "Mandarin" is really itself a fuzzy category that starts falling apart when you poke a its seams, but really that's just the nature of language. "English" starts falling apart when you poke too hard at its particular words as well.
The central point about the embedding of Mandarin though is that it reads completely fluently to a Mandarin speaker. It's not a pidgin, it's not a situation where the Mandarin speaker can understand it in bits and pieces. It reads like anything a Mandarin speaker would have written.
For modern Cantopop, the recent putsch to match more closely to spoken Cantonese is due to an increasing dislike of Mandarin among the young in Hong Kong.
Ooo... that's interesting. I knew that there's been a rise in regional dialect pride in general and that Hong Kong in general has never really been too fond of the Mandarin-speaking Chinese tourist masses, but hadn't realized it'd spread to modern Canto-pop. Might have to take a gander at some of the latest songs.
[1] https://en.wikipedia.org/wiki/Taiping_Rebellion#Taiping_Heav...