Eszett (ß = German sharp S)

Eszett (ß = German sharp S)

In the German alphabet, ß (Unicode U+00DF) is a consonant letter that evolved as a ligature of "long s and z" (ſz) and "long s over round s" (ſs).

The combination of long s and s is also seen in Early Modern English (example from the US Bill of Rights)

Since the German spelling reform of 1996, both ß and ss are used to represent /s/ between two vowels. In alphabetizing German words, the collation rules say to treat ß as a double "s". 

Source: http://en.wikipedia.org/wiki/%C3%9F

If locale-based string comparison is not available, converting to UPPERCASE is better than lowercase. For example,

uppercase("Straße") == uppercase("Strasse") == "STRASSE"

lowercase("Straße") != lowercase("Strasse"), because "straße" != "strasse"