As you can notice nobody calls in Russian Francesco d'Assisi Франческо д'Ассизи - and I'm not saying this in ironical way. For instance, Leonardo da Vinci is indeed called
Леонардо да Винчи. The thing is that traditions of transliterating names are not straightforward - some names are transliterated more or less at they "are", some names - do not.
This holds true even for the name originally coming from the same source language. For instance, in Russian we refer French kings named Henri as
Генрих though actually one rather can expect them to be named
Анри. The same with
Карл - who quite often were actually Charles (Шарль).
At the same time we have
Эркюль Пуаро, not Геркулес Пуаро. Or
Артюр Рембо, but not Артур Рембо.
This is because names of some historical persons come for us through some other mediator language. In case of
Генрих it obviously was German.
In case of
Франциск it was actually Latin - in Latin it's Franciscus - strictly speaking we don't know for sure how
ci is supposed to be read in Latin. In fact, even in modern Italian to my knowledge there are some dialects where
ci is pronounced rather as /t͡s/ than /tɕ/. There are different traditions of pronouncing Latin words - one of them to pronounce
сi as /t͡si/ - and this is actually a German tradition of Latin pronunciation. Here's an excerpt from the Wikipedia article dedicated to this issue:
Historically German school of pronunciation of Latin words was widely adopted in Russia. This how San Francisco ended to be
Сан-Франциско in Russian. It comes from that times when even Francis Drake who's now
Френсис Дрейк was referred as: