Found this on Wikipedia:
"Sasha originated in countries of Central, Eastern and Southern Europe as a diminutive of Alexander and Alexandra. It is also found as a surname, although this is very rare. Alternative spellings include: Саше (Macedonian), Sa?a (Slovenian, Serbian, Croatian, Czech, Slovak, Lithuanian), Sasza (Polish), Sashko (Ukrainian), Sascha (German), Sasja (Dutch), and Sacha (French).
This name is especially common in Europe where it is used primarily by males as a diminutive of Alexander, although females may also use it as a diminutive of Alexandra. Despite its popularity in informal usage, the name is rarely recorded on birth certificates in countries such as Russia, Ukraine, the Czech Republic, and Slovakia, as it is considered a diminutive and not a formal name. Exceptions are Serbia and Croatia.
In Germany, the civil registry offices allow the inscription of Sascha in birth certificates as a formal name but only for boys."