I am thinking about making an introductory book to some different "languages", for self learning. But I realize I'm blending the writing system with the pronunciation system, and am starting to get confused. To help ease the confusion, I am wondering if technically it's possible to write any language down using any script (so for example, write English using Hebrew Script, Write Sanskrit with Arabic Script, I guess you can't write English with Chinese Script so there's a counter example I just realized, but still I would like to ask to learn more).
Basically I started with the idea for a "Simplified Hebrew Grammar". I was going to start by taking the letters (symbols/orthography) and writing the pronunciations. But then after a few hours of trying that I realized the Hebrew letters sometimes have multiple pronunciations depending on context. Then I think about English, which uses the Latin script, and you pretty much can't say what the pronunciation of a single letter is without resorting to it's surrounding context in a word or something. The letter "a" isn't "ah", it's "cat", "father", etc.
So then I thought about well what if you had books on (1) Scripts and second books on (2) Pronunciation, or writing using a particular script.
But say you had a book on the Latin orthography. Other than how to actually write the letters (imagine kindergarten templates/guides), it doesn't seem there is much to say about them. They represent sounds all over the place, depending on the natural language being spoken, the dialect, etc. What else can be said of a writing system other than just how to literally do the calligraphy?
Anyways, so then it seems like "we're back to a book combining both orthography and pronunciation" again... Like an "English" book, or a "Spanish" book, not a "Latin Orthography" book.
But then I think of writing systems like Devanagari, which seems much more robust and refined. Each letter/shape has a specific sound, which is modified only according to specific rules (for the most part?). In this case, you could write a book just on "Devanagari" and mapping each letter to pronunciations (a short kindergarten book). So this is why I started to ask this question here. In Devanagari (or Sinhala, or other "Southeast Asian" languages), you can write most other languages it seems to me.
My question is, which writing systems can be used to write other languages? Can these writing systems write all other languages or only some? And which writing systems can't write other languages (like Chinese)?
As a tangent, then I'm imagining if there is ever a language where a letter such as
b is pronounced
/b/ in one context, and
/h/ in another, and
/t/ in another, just to make things even more complicated. But just a tangent lol.