I just realized that there is a section called "Gothic Editing"
I am so sorry, I automatically went to the Gothic 2 section and browsed there, but not elsewhere. If this topic is at the wrong place, please replace it.
I just tried to use the Diakreion Texture Converter, but somehow it didn't worked for me.
I loaded the image (tried bmp and tga)
selected "automatic conversion" (also tried with "show only")
"to format:" selected .TEX
also "2-A8B8G8D8R8" (also tried with all the others)
Mipmaps set to 1
Clicked to "text"
Clicked to "export"
nothing happens
But maybe I am really dumb...