If the schema has an entity MyMain with all its fields i18n and an entity MySecondary related to MyMain and you try to create a new MySecondary item using Symfony forms you get an error.
I think the error is doctrine and in i18n because if you remove a field from the i18n behavior (fields: [a,b,c,d], for example) all works ok.
I've included a symfony project to help developpers replicate the error.
And the form code
And last the queries (and its order when you get the error)