When you change the default language of a Web Content, then the original content will be added as a translation. However the non-localizable fields in this translation are still able to be edited, while they should be allowed in the default translation only.
1. Go to Site Administration --> Content --> Web Content, here create a structure, name the title "test" and copy the below code inside the source, and finally save.
2. Add a template to the structure.
3. Create a web content with the new structure, fill out all the necessary fields and publish the content (use the default language English-us ).
4. Edit the content and change the default language to German.
Result: If you open the English translation the content from the NonLocalizableText is editable.
Expected Result: Because the field has a non localize characteristic we shouldn't have the possibility to modify the content.
Not reproducible on master.