Detect untranslated strings

[mondeja]

This is done in the i18next ecosystem through the ESLint plugin https://github.com/edvardchen/eslint-plugin-i18next

I'm thinking on two possibilities here:

• A custom lint rule executed by DyLint (see https://github.com/trailofbits/dylint)
• Add another option like check_translations, probably named check_untranslated or something like that.

The solution will depend on the amount of false positives and how to handle them.