Note that rules are different for different languages, even among those using Cyrillic. E.g. letter "г" is "h" in Ukrainian, but "g" in Russian. "И" in Russian is "i", which is a letter on its own in Ukrainian, while Ukrainian "И" is transliterated to "y".
You should also bear in mind that English isn't quite that simple either. That г is a Greek gamma around here and hence "G". (it isn't really) Now it's funny you mention И -> y etc.
German and English and Dutch are often called Germanic languages. For example kirchegaard -> has an obvious route if you squint to: "church yard". Often y -> g or d -> g. So day becomes tag. The German word for (Eng) day is tag. "Guten tag" ... gooden dag/gudden tag and other spellings is middle english for "good day".
There is a town in England called Weybury. There is a town in Germany called Wegberg. G -> Y. Almost certainly that is bollocks but it makes a nice story. The burg and bury bit is probably right - a fortified town. Wey -> Weg is probably wrong even though way and weg (that means way in German too),
FTR, SSOU 9112:2021 (ukr. "DSTU 9112:2021", transl. "DSTU 9112:2021") is a an actual official State Standard of Ukraine for official transliteration:
> From 01.04.2022, the national standard DSTU 9112: 2021 comes into force: «Cyrillic-Latin transliteration and Latin-Cyrillic retransliteration of Ukrainian texts. Writing rules». The standard was proposed and developed by specialists of the State Scientific and Technical Library of Ukraine and the Technical Committee 144 “Information and Documentation”.[0]
According it there are two variants inside this standard (see comparison[1]):
1. ДСТУ 9112:2021, Система А (system A) — letters represented with "Basic Latin" and some characters with diacritical marks from "Latin-1 Supplement", "Latin Extended-A" Unicode Blocks):
1.1. Київ, Україна - Kyїv, Ukraїna
2. ДСТУ 9112:2021, Система Б (system B) — all letters represented using only "Basic Latin" Unicode Block:
In latest version it is possible to choose official ("ДСТУ 9112:2021") or any other exists variants[0] — in extension option (click on extension icon on browser toolbar):
> Switch Latinization system in the popup window.[1]
