EZP-26751 issue, it's not possible anymore to edit and change content of content attributes according to what is described in the documentation:
When a Field is not flagged as Translatable, its value will be copied from the initial/main translation when a new language version is created. This copied value cannot be modified.
Now, if a translation is created from a content type with an attribute which is mandatory and not translatable, and if the translation is not based on the original language, it won't be possible to publish that translation since the attribute will be empty, can't be edited and it's mandatory.
- Create a new content type with a "mandatory" and "not translatable" attribute
- Create a new content object from that content type
- Create a new translation of that object not based on the existent translation.
- Try to publish the draft