I am not familiar with WPML but if I get you right another possibiliy may help by
using the plugin “Dynamic Widgets” as you can
1. open the “text” widget
2. insert e.g.
3. place it in “banner header”
4. use the dynamic widget to chose the sites you want it to appaer
Works fine with the plugin Polylang that also provides me a checkbock to chose if it should appear for all languages or a specific one, within the widget.