In languages with accents, an all-cap layout can present problems: they get in the way.
There are a couple of "cheats" .
In French, for instance, using a Didot face, the grave, acute, and circumflex may become a thin horizontal line, with context providing sufficient cues for the reader. Some typographers will even leave the accents off completely.
In German, the umlaut appears in only two cap characters, the Odieresis and the Udieresis. Consequently, there is the marvelous "Mickey Mouse" Odieresis of Futura Extra Bold (not available in digital).
My question is: do the Odieresis and Udieresis only appear in German? If so, does it make sense to give these characters "dropped" accents in the standard Latin encoding? Here's what they would look like in a display Roman. 


