In relation to How to build a robust transliteration scheme across languages? I am now confused about orthography-to-IPA mappings, such as for Turkish. When you see the orthograph like the letter
a mapped to the IPA value
/a/, what does this mean? Does it mean in the "general" case? In the ideal case? In a mainstream case? Because (and I don't know for Turkish, but for English)... Well, English's situation is the craziest I've seen. So my question is, how should I be using these orthograph-to-IPA mappings? As the gold truth? As a rough guideline? As an entrypoint to further research in some textbook? Why do they even put it there if it's not the gold truth?
I ask because I want to build a transliteration (or perhaps transcription? pending the above question) system for various languages. I want to result in the latin alphabet for pronunciation purposes, so I've been using these orthography-to-IPA tables (all the southeast asian and asian languages have simple ones, for example). But now I'm not sure what they represent. I would like to know what they represent, and what I should be doing instead, to capture such information to create a latin text version of some language/script for purposes of pronunciation.