String Translation allows you to translate texts that do not belong to any post. You will be able to translate the site's tagline, widget titles, texts in the theme admin, plugins and anything that uses GetText for localization. Related documentation:
Problem : I have translated a custom post type under WPML >>> Translation Management, but it still shows wrong at the frontend. Solution : It is very likely that the .mo files in the theme already have the translation for the custom post type. In order to fix the issue you need to delete the translation of the custom post type from the .mo file. Since it is already translated in WPML >>> WPML Translation Management >>> Multilingual Content Setup > Custom Posts the two translations are in conflict.