Does Cydia only work properly, when the iPad language is set to English?
In a short test of mine, did Cydia refuse to install SBSettings when the language was not in English, some error about not being able to locate a file showed up. Setting the language to English during the installation and then afterwards back to another language works fine as a workaround. I just don't see, how the iPad display language would prevent the app to install, unless this is normal behavior for apps, which don't come in the set language.
Is this what usually happens?