Translation string loading order
When GravityView loads translations, it looks in the following locations in the following order:
/wp-content/languages/plugins/gravityview-{locale}.mo
(loaded by WordPress Core)/wp-content/mu-plugins/gravityview-{locale}.mo
/wp-content/mu-plugins/languages/gravityview-{locale}.mo
/wp-content/plugins/gravityview/languages/gravityview-{locale}.mo
If you want to override translations, place them in any of the first three directories using that naming structure, then deactivate the plugin and activate it again to ensure the new translation files are properly loaded.
Since GravityView version 2.16, the text domain has changed to "gk-gravityview".