Blondie did this, and it seemed an interesting idea, so here are my picks off the top of my head. I'm going by original title rather than translated title for the films not in English, e.g. Osaka Elegy is N, as its real title is Naniwa erejii. More broadly, I'm going by the title on the film, not by whatever title Letterboxd has it under, so For Marilyn is U, because the title on the film is Untitled (For Marilyn). Letterboxd has a lot of other films called Untitled in its database, I don't know why this one is listed differently.
Easy mode: like 99% of all film guides, I'm ignoring the words "a" or "the", or their equivalents, at the start of titles.
I know Murnau should be here but isn't. Like I said, off the top of my head as of hitting Save.