You can translate a string that does not exist in post, pages and taxonomies using Dashboard → WPML → String Translation section.
String Translation Example
We will learn how to translate site name, Which is "Theme Test" for this example.
Go to Dashboard → WPML → String Translation section and search for "Theme Test".
Once found, Translate it as displayed below.
Translate the tag line using the same search.
Now view the front end of your other language home page and you will have the site name and tag line translated.
So, You can translate all strings that are out of post's or page's content area.
String Translation by Translation Domain
You can also choose a specific translation domain to precisely translate the strings attached to only a specific translation domain as shown below.
Customizer Strings Translation
You can also translation the strings of Customizer in String Translation section.
To shortlist or find any Customizer string you can click on string with domain and translate all the strings starts with admin_texts_ because these are Customizer strings.