The reason this happens is that the devs are using a file called DownloadFilesList.txt that lies in the game's directory to check version of splash screens against their current version.
The problem is that they wrote the paths all wrong. They are using relative paths: "raw\en....."
I'm a programmer and there are 2 things wrong here:
you should never use "\" in paths strings. always use "/". that cause it to be cross platform.
secondly, the dev forgot to add one more "\" at the beginning of the strings. so when they search they search for (for example):
"c:\games\ddo" <--- game's directory
"raw\en...." <--- relative path
which when you concat them turns to: "c:\games\ddoraw\en"... which doesn't exist.
This explanation, I hope, will make the devs finally fix that bug. In the meantime, for all your players out there do the following:
go to that file i mentioned, delete all the files (including the corresponding opening <file> and enclosing </file> tags) for all languages you dont care for. leave the language you care for and add a "\" at the beginning of each file right before the word "raw" (if you are on mac add a "/" and not a "\").
right click on the file and mark "read-only".
from now on ddo cannot touch that file and it will always make sure your relevant splash screens are up to date without annoying you each time you start the launcher.

devs, it's easy to fix, plz do.