In Minecraft version 1.8 the game used one translation string when a block or item name was invalid:
However at some point this translation was replaced by two new ones (very likely in version 1.8.1):
Even though they were added for an official release they are untranslated for all languages other than "English (US)" and are not listed on crowdin (website used for translations) either.
- Open Minecraft 1.8.9 which should have translations for all game elements
- Set the language to something different than English
- Use the following command