This article is about a failure to do normalization properly and is not really about an issue with Unicode. Regardless what some comments seem to allude to, an Umlaut-ü should always render exactly the same, no matter how it is encoded.

There is, however, a real ü/ü conundrum, regarding ü-Umlaut and ü-diaeresis. The ü's in the words Müll and aigüe should render differently. The dots in the French word are too close to the letter. In printed French material this is usually not the case.

Unfortunately Unicode does not capture the nuance of the semantic difference between an Umlaut and a Tréma or Diaresis.

The Umlaut is a letter in its own right with its own space in the alphabet. An ü-Umlaut can never be replaced by an u alone. This would be just as wrong as replacing a p by a q. Just because they look similar does not mean they are interchangeable. [1]

The Tréma on the other hand, is a modifier that helps with proper pronunciation of letter combinations. It is not a letter in its own right, just additional information. It can sometimes move over other adjacent letters (aiguë=aigüe, both are possible) too.

Some say this should be handled by the rendering system similar to Han-Unification, but I strongly disagree with this. French words are often used in German and vice versa. Currently there is no way to render a German loan word with Umlaut (e.g. führer) properly in French.

[1] The only acceptable replacement for ü-Umlaut is the combination ue.