Why are my special characters not displaying properly?
A font experiencing issues displaying special characters is more than likely due to the fact that many font libraries do not implement anything else other than the standard Latin Characters.
As you can see from this example, the special character in question is the umlaut [double dots over letters]. This displays correctly over the 'a' it is causing problems over the 'u'.
It is misaligned over the 'u' due to it's placement next to a capital letter.
This misalignment is forcing an increase in space between the 'u' and 'n'
The only way to avoid these kinds of font typographical problems is to fully test any font library you may want to use, in your chosen language.