I believe the most straightforward approach is to remove language versions directly in Sitecore databases, followed by rebuilding all caches and indexes.

1) Execute the following queries on your Master and Web databases:

<!-- language: lang-sql -->

	DELETE
	FROM [VersionedFields]
	WHERE [Language] = 'fr-FR'

	DELETE
	FROM [UnversionedFields]
	WHERE [Language] = 'fr-FR'

2) Clear item caches on all instances using the page `/sitecore/admin/cache.aspx`

3) Rebuild the link database on all Sitecore instances. You can do that from the control panel.

4) Rebuild search indexes on all Sitecore instances. You can do that from the control panel.