The patron interface for Ebook Central is available in eleven languages:
Czechčeština
FrenchFrançais
Japanese日本語
PortuguesePortuguês
Chinese (simplified) - 简体中文
Chinese (traditional) - 繁體中文
English
GermanDeutsch
Korean한국의
SpanishEspañol
TurkishTürkçe

To set your preferred language for the patron interface, select  User-added image from the top-right of the screen, then select "Language".  Click the radio button to select the desired language.  Then click "Save Changes"