- Create de.yml with German translations
- Create fr.yml with French translations
- Create es.yml with Spanish translations
- Create it.yml with Italian translations
- Update generator documentation to list all available locales
- Add generator tests for new locale files

All locale files maintain identical structure with 78 translation keys
covering inputs, internals, outputs validations and error messages.

- Add full assertion matrix: each test verifies its locale exists AND all other 5 locales don't exist
- Remove file_content/expect(content).to include assertions
- Update test descriptions to "copies only X locale file"
- Add new locales (de, fr, es, it) to assert_no_file in default and en tests