[This link will merge with the text and the 2nd link] non-link text [this link causes the previous link to merge with it.] : http://example.com/ : http://example.com/áéíóúö/
Note that there are client side and server side bugs with this.
Server side: when rendered the above is one link, pointing to http://example.com/
Client side: when previewed only the first link is linked.
I'm primarily concerned about the foreign alphabet characters since they are the most frequently used, not other glyphs that may be used in URLs.
As I've said elsewhere:
Sometimes URLs can fail to link correctly because they contain disallowed characters. In these cases encode the characters using the % notation. Previously characters such as ()  ' and * were not allowed but the server-side Markdown renderer has been modified to accept them now. Currently the only (known) characters that aren't accepted are ones with accents, graves, diaeresis etc. For example: é or ö, although with wikipedia links you can just use the unadorned character.