I'll pass this translation note on to Jason for you. Otherwise, at least for the background image, go to Tools -> Options then Default Background on the left. I've personally set this to use my wallpaper, but you can set it to a specific image. Then, once you have it set to what you want (though you can also use the default background), go up a few options to Background Priorities and uncheck all of the boxes here, or check for just the ones you want. Image Priorities is a premium feature though.
To your library performance, you do have a really large library, and while we're not certain it's a bug or users computers, we do know it's an issue that keeps cropping up. Turning some things off can speed it up a bit. Making sure LaunchBox isn't caching (and with a 40k library that COULD take a while), Less images to load will help (so editing image priorities for the background could help), and less information in the game details bar (even if you don't use it, that could potentially help as less info needs to be loaded on demand). Turning off auto-playing music and video can help too, and potentially disabling the controller support for LB. It's really hard to nail it down to one specific thing, so if you do those settings individually and performance increases let me know. I am surprised you don't have performance issues in Big Box though... that is surprising. Did your Big Box finish caching by chance?