Add filter option (default: "i18n") to search against

without filter in your grunt task configuration:
{{ 'ACTION.DELETE' | i18n }}

with filter: "translate":
{{ 'ACTION.DELETE' | translate }}
Documentation about JSON supported format

(https://github.com/yllieth/grunt-angular-i18n-finder/commit/35df7cc86c9bbb22d6e289a5a709d677e503bed8)