First lookup the i18n key by calling the getSystemTextMapping(String key) method from the class ModelerAPI. Subsequently the translation can be retrieved using Core.getInternationalizedString(IContext context, String i18nKey, Object ..args) or Core.getInternationalizedString(String languageCode, String i18nKey, Object ..args). The arguments parameter is optional here (can be used for template variables).
A code snippet illustrating this procedure:
String i18nKey = ModelerAPI.getSystemTextKeyMapping().get("mendix.widget.MxDataGrid.true");
String translation = Core.getInternationalizedString("en_US", i18nKey);
The translation of the boolean value 'false' can be found using the key "mendix.widget.MxDatagrid.false".