Steps to reproduce:
- Go to Content & Data > Web Content and click on the Structures tab;
- Click to add a new structure;
- Drag a Select from List field to the structure's body and add one or more options to it;
- Select a new language besides the structure's default;
- Only add a translation for field's label;
- Try to save the structure.
The structure is successfully saved.
Note: this happens because no translation was added to the options either. A user shouldn't have to edit the options when adding a translation to the structure.