There is no extension able to load the configuration for "_translation_webui"
# config/packages/php_translation.yaml
translation:
locales: ["en"]
edit_in_place:
enabled: false
config_name: app
configs:
app:
dirs: ["%kernel.project_dir%/templates", "%kernel.project_dir%/src"]
output_dir: "%kernel.project_dir%/translations"
excluded_names: ["*TestCase.php", "*Test.php"]
excluded_dirs: [cache, data, logs]