The \assets\resources\<language> folder in the Magellan engine contains all the json files which the engine uses to fill dynamic text on the site.
The locale information on the end users browser selects which (language) folder and json file is used. For multiple language Magellan sites, a user can also manually select the desired language from the dropdown menu on the top right of the site.
Do not modify the Magellan engine json files. Instead, add a copy of a language file to <your theme name>\assets\resources\<language> folder and make changes. The theme file is used on book publish.
Each applicable language must be updated separately, using the same process.