Set a language as a fallback for the chosen language (e.g. "Deutsch" as a fallback for "Deutsch (Sie)")
Starting with WordPress 4.3, you can use languages such as “Deutsch (Sie)” (formal German) in your WordPress installation. But if the themes or plugins you are using do not have a
translation file for this language, WordPress would use the default language, usually English, instead. With the help of this plugin, you can set a fallback for your chosen language.
Every time a translation file is loaded, the plugin will then load the fallback if a translation for the originally chosen language was not found.
A list of all my plugins can be found on the WordPress Plugin page on my blog kau-boys.com.
Screenshots

Screenshot of the settings page
FAQ
Does this plugin only work with formal German?
No. You can choose any fallback language that fits your original language. Think about fallbacks from “Spanish (Mexico)” to “Spanish”.
Do I need to manually install the fallback language?
No. The plugin will automatically download the fallback language if it is not already installed.
How can I report security bugs?
You can report security bugs through the Patchstack Vulnerability Disclosure Program. The Patchstack team helps validate, triage and handle any security vulnerabilities. Report a security vulnerability.
ChangeLog
2.1.1
- Fix wrong version number in PHP file and readme
- Time invested for this release: 10min
2.1.0
- Add
sanitize_callback for setting
- Increment Tested up to
- Add link to Patchstack in readme
- Time invested for this release: 30min
2.0.1
- Fix some minor Plugin Check issues
- Increment Tested up to
- Time invested for this release: 20min
2.0.0
- Implement a solution for “_load_textdomain_just_in_time” function not loading the fallback “.mo” files
- Time invested for this release: 150min
1.0.5
- Increment Tested up to
- Time invested for this release: 10min
1.0.4
- Remove the languages folder and prepare the plugin for automated deployments
- Time invested for this release: 10min
1.0.3
- Implementing the fallback locales as an array
- Time invested for this release: 10min
1.0.2
- Bumping version number
- Time invested for this release: 2min
1.0.1
- Small bugfix for the filter
- Time invested for this release: 15min
1.0.0
- Initial release of the plugin
- Time invested for this release: 200min