For extracting the messages from the UI components, run the following script:
$ npm run generate-pot
This script will generate a template.pot file, which contains all the strings from the application ready to be translated. Upload this file to your translation tool, translate the strings and after that, export the .po files for all the translations and place them into i18n folder.
For generating language files which are used by the application, run the following script:
$ npm run generate-language-files
Now your translations are updated and ready to be used.
The default language is set to be en. This configuration can be overridden in config.js by changing the defaultLanguage field. Change this only to a language that is supported by the application (is present in the supportedLanguages list).
After your first visit to the application from a browser, the application will remember the current language state. In order to change the defaultLanguage field and see the change, you should clear the localStorage entry language from the browser.