Add clarifying sentence about .json files

docs/source/development/i18n.md

@@ -29,6 +29,7 @@ The workflow for creating *new* translatable text strings is as follows:
 1. Run the unit tests as described in {ref}`run-jest-tests-on-volto-core-label`, following the prompt to update the snapshot when the test fails.
 
 This way of organizing translations relies on [gettext](https://en.wikipedia.org/wiki/Gettext), a proven and established system with great tool support.
+`.json` files in react-intl are equivalent to `.mo` files in gettext.
 
 All translation files are located under the directory [`packages/volto/locales`](https://github.com/plone/volto/tree/main/packages/volto/locales).