Bonjour Emmanuelle,
I don't know if you can have a different banner be pulled up depending on the language version of the website. My workaround would be to have an image or graphic-only banner and to use text boxes overlays for the event title etc. - those would be language-dependant. Please note that it's also usually better not to have text on pictures for both accessibility reasons (not readable by screen readers) and for responsive design (the picture gets resized and cut off when seen on different sized screens).
J'espère que c'est utile !
Cheers,
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Béline Falzon, CMP
Assistant Director for Events
Stanford University, Precourt Institute for Energy
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