Thanks for the clarification and the pm, giver888. I have installed the files meanwhile (no change to executables or registry settings, by the way). If you extract the new files to a temporary folder and backup the (4) game folders affected, you can easily revert the game back to the original state.
My compliments to the author of the subtitle mod - must have been a huge amount of work! With the exception of a few spelling and grammar errors (no surprise, considering the sheer volume of the texts), everything looks excellent. I noticed one consistent (minor) issue: The German umlaut "ü" is missing everywhere (suppressed by the system, I guess). Like in "Küche", which is printed as "Kche". "ö", for example, has been changed to "oe", and gets printed.
But like I said, this isn't a big deal, no need to correct it, as far as I'm concerned.
Still, I'm pretty sure that I used to have an older subtitle mod, probably in English, which simply adds subtitles to spoken text. A shame that I can't find the file.