Later, when it comes to foiling the Basterds, Landa just gets lucky. As in, he finds a napkin with the name, autograph, and fresh lipstick of the Basterds' mole at a crime scene with three dead Basterds. They may as well have thrown in her dental records and a signed confession. Then, even with all of those advantages, Landa needed to coincidentally be fluent in Italian to be able to spot the disguised Basterds when they pretend to be Italian. That's not genius detective work; that's applying your experience from a year abroad.
Even sillier, the movie actually does feature a good detective: Dieter Hellstrom, who effectively sniffs out the German-speaking Basterds by noting their accents and foreign mannerisms. But somehow Landa was the one who got the reputation for his incredible observational skills.