WPML is a premium WordPress multilingual plugin.
To get started, you will need WPML and add-on Plugins i.e. the core WPML Multilingual CMS which is always required and the String translations add-on. Information on installing & activating WPML is available on the WPML getting started guide.
14.1 How to set and translate main features of the theme
Using translation management http://wpml.org/documentation/translating-your-contents/using-the-translation-editor/
Translation Management & Features – http://wpml.org/documentation/translating-your-contents/using-the-translation-editor/translation-management-features/
Translating URL slugs – http://wpml.org/documentation/getting-started-guide/translating-page-slugs/
14.2 An example of how you can translate strings coming from the theme
How to scan strings coming from the theme – http://wpml.org/documentation/getting-started-guide/theme-localization/
How to translate strings using String Translation – http://wpml.org/documentation/getting-started-guide/string-translation/
When selecting a panel inside the Customizer you need first to translate the pages that you want to feature inside the panels and than after selecting page in Customizer, you'll need to translate the strings by placing the translated page IDs.