Delete Entity Translations
This module allows you to delete specific content translations for a chosen language before deleting the language itself, preventing data loss. It provides a configuration page to select the language and entity types for deletion.
Overview
Deleting a language will remove all interface translations associated with it, but content in this language will be set to be language neutral and will not be deleted. The Delete Entity Translations module allow to delete entities and their translations for selected language before removing the language itself.
How to use
Go to admin/config/regional/delete-entity-translations, select the language with entity types you want to delete and run the process of deleting entities / translations. Here more detailed documentation with screens