Here stat
is a reference to the POSIX standard call of that name, stat(2)
.
Perhaps you can take some clue from the manual page's description, the brief one is "get file status".
My German is waaaay too rusty to suggest a translation, but inserting it into the English would give "Unable to get file status (stat) %s\n" (I kept the original "stat" phrase since it's highly-detailed technical information and might be useful).
You could of course not try to work around the function name, and instead just say "The stat() function failed for %s", it's the use of the funtion name as a verb which makes it harder to translate, I think.