Detect unused keys

[saschb2b]

Thank you so much for this project!
I use it in combination with https://www.npmjs.com/package/eslint-plugin-i18n-json for json specific checking.

I was wondering if you could also detect unused keys like the eslint rule for vuejs https://eslint-plugin-vue-i18n.intlify.dev/rules/no-unused-keys.html#rule-details