Update docs/multisite/languages/back_office_translations.md

Author: adriendupuis

docs/multisite/languages/back_office_translations.md

@@ -120,4 +120,5 @@ The language to display will then be selected automatically based on [user prefe
 
 !!! note
 
-    Run `composer run post-update-cmd` which install your translations to JavaScript through Bazinga, and also clear the cache.
+    Run `composer run post-update-cmd` which both install your translations to JavaScript through Bazinga, and clear the default SiteAccess cache.
+    Run `php bin/console cache:clear --siteaccess=admin` to clear the Back Office cache (adapt SiteAccess name if needed).