customLocale error

Using the customLocale-plugin: when I try to open the “Locales” tab in “Website Settings”, I get the following PHP error in the apache error log:

PHP Fatal error: Uncaught Error: Class ‘PKP\controllers\grid\GridHandler’ not found in /var/www/html/plugins/generic/customLocale/controllers/grid/\n
Stack trace:\n
#0 /var/www/html/lib/pkp/includes/ require_once()\n
#1 /var/www/html/plugins/generic/customLocale/ import(‘plugins.generic…’)\n
#2 /var/www/html/lib/pkp/classes/plugins/ CustomLocalePlugin->setupGridHandler(‘LoadComponentHa…’, Array)\n
#3 /var/www/html/lib/pkp/classes/core/ HookRegistry::call(‘LoadComponentHa…’, Array)\n
#4 /var/www/html/lib/pkp/classes/core/ PKPComponentRouter->getRpcServiceEndpoint(Object(Request))\n
#5 /var/www/html/lib/pkp/classes/core/ PKPComponentRouter->route(Object(Request))\n
#6 /var/www/html/lib/pkp/classes/core/ Dispatcher->dispatch(Object(Request))\n
#7 /var/www/html/index.php(68): PKPApplication->execute()\n
#8 {main}\n
thr in /var/www/html/plugins/generic/customLocale/controllers/grid/ on line 27, referer: Einloggen | Global Europe – Basel Papers on Europe in a Global Perspective

I tried it using plugin versions, and my own modification (GitHub - edelm/customLocale: Fine-tune the language of OPS, OJS, or OMP without modifying files or changing it for everyone.), all with the same result.

Does anybody habe any idea on whats going on?