@Dolomie: In Full Frame Pro version, you can make Promotion Headline and Sub-headline text multilingual by using String translation from WPML plugin.
So, first change the text default text in “Appearance => Customize => Theme Options => Promotion Headline Options” and save it. Then go to “WPML =>String Translation” and then translate it. If you don’t see that Promotion Headline and Sub-headline text, then in “String Translation”, you can click on “Save options and rescan strings” button. For more about string translation, check this out https://wpml.org/documentation/getting-started-guide/string-translation/