Until the 19th century, J was used instead of I in diphthongs, as a replacement for final "-ii", and in vowel groups (as in "Savoja"); this rule was quite strict for official writing.
До XIX века "J" использовалась в дифтонгах вместо "I", вместо заключительного "-ii" и при разбиении группы гласных (как в слове "Savoja").