Currently, there is no way to edit an existing Content Type via Admin UI if the main language of the "Admin" siteaccess is changed. After displaying the edit form for the Content Type, all "Name" form fields (for Content Type and for all of its Fields) are empty, which prevents saving the form. Even if the "Name" form fields are filled, submitting the form results in the following validation errors:

Content type name cannot be blank and cannot exceed 255 characters.
Field definition name cannot be blank cannot exceed 255 characters.
Field definition name cannot be blank cannot exceed 255 characters.
(...)

This issue is not reproducible on eZ Platform v1. "Name" form fields are filled there and the form can be submitted without an issue.

Steps to reproduce:

1. Create new ez Platform v2 installation.
2. Edit app/config/ezplatform.yml file and change the following configuration:

   ezpublish:
       system:
           admin_group:
               languages: [eng-GB]
   

   to the following:

   ezpublish:
       system:
           admin_group:
               languages: [ger-DE, eng-GB]
   

3. In Admin UI, go to Admin -> Content Types -> Content. Edit "Article" Content Type.
4. You will notice that the "Name" form fields are empty. After filling them and submitting the form, the validation errors mentioned above will be presented.