In the past, I had worked on different websites and app that support localization. The user on these sites can work with the language of their choice and translations were provided on UI elements for selected languages.
When working with translation files for multiple languages, I found that there were instances when developers added translation text for English but forget to add translation text for languages other than English. That was a problem when a user chooses to work with a language other than English (He/she was provided with misleading text).
Secondly, there were issues due to duplicate translation keys provided by developers. It leads to incorrect translation due to overwriting (Misleading!).
I learned that adding the test for verifying these rules will help developers to identify the problems before pushing changes to production.
The simple react application is hosted on github: https://github.com/way2datta/translation-demo.
This sample app has support for English and Hindi language. The app has tests for verifying the translation files.
When the translation keys are present in the all translation files. The test runner display everything is well.
When I add translations in one language file and forgot to add it to another language file, tests start yelling at me.
Thus, the tests for translation files can help the developer to identify the issues related to translation files in development phase itself.