Missing Translation Fallback Language
This module enables you to specify a default language to fall back to when translations for a specific language are not found. This is useful for websites with multiple languages where some content may only be translated into a primary language, which can then serve as a fallback for other related languages.
The Missing Translation Fallback Language module allows you to set a fallback
language to use when translations are missing for a specific language.
For example, you have a website with two configured languages, Dutch and Flemish.
For some words there are specific Flemish translations, but for most of the strings
the Dutch translation will do. You can set the Dutch language as a fallback for
the Flemish translation.
Installation and configuration
Install as you would normally install a contributed Drupal module. After that,
navigate to the /admin/config/regional/language page and optionally configure
a fallback language for each language.