There’s a useful trick that I first read about from a Microsoft developer, but I can’t remember which. If you want to confirm that your application properly handled international characters, put the following into it: Iñtërnâtiônàlizætiøn
Lots of non-English characters, but still readable. Since I can never remember what this phrase is, I’m recording it here for my future self.
(Update, 22-10-2013: Mathias Bynens talks about extended Unicode characters, like “pile of poo”, and a combination of the “Iñtërnâtiônàlizætiøn” string, “Ādam” (from the comments; contains a non-Latin-1 character), and “💩” U+1F4A9 PILE OF POO (an “astral plane” character) makes a useful smoke test: a quick way to know that you’ve failed.)
(Note that at this writing, I can’t put the “pile of poo” directly into
the Wordpress 3.6.1 post editing box: I have to use the HTML Unicode
escape 💩 because Wordpress cuts off the post at the character
if used directly!)