Before (I don't remember which version it was changed with), the English language was always by default, even on a multilingual site that does not use the English language.
It was then a constraint because any form had to be created in English and then add the translations for the other languages. It was unnecessary and restrictive.
After a French-speaking user reported this problem to Mr. Bopp, BF was changed so that the main language of the site became the default language for forms.
Updating to the latest version has most likely caused this reversal.