You can create your own language as needed in order to display your website in other languages.
For example, to modify Postcode text to Zipcode, go to Developer->Translate. Chose language and click the Select button. Click application_lang.php file, search and replace Postcode with Zipcode and click the Save button.
If any field is not translated, the application will load the content from the modules (e.g. listings) table. This information will be shown in the default language field (language set under Settings->Settings->Main Settings tab). If the default language is set to French, then all the entered information will be displayed in the French input field only. The user has to enter information separately in the English input fields to view the title/slug etc.