Hi Kev.

For one of my TV shows, I have a foreign language banner displayed.

Is there a way of amending it please?

I also have some shows without a banner, so it would be nice to add one.

Banners are fetched through the API. SB/Sonarr fetches it from tvdb. If the TVDB doesn't have them, you can add one. If it has one in a different language you could try to refresh the show and see if it pulls a new one, or you can browse to the sickbeard data folder and replace it manually.