I don't know about the former, but I can answer the latter (and the presumably implied question of why doesn't Unicode cover what should be a fairly common use case?).

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.