I have just installed Apache OO 4.1.1 on my PAF platform. The intaller's langauge was English. After the first start the progam's GUI language was set to US-English. I changed it to German. After a program restart the GUI was partially English (the first selection screen was in English), the menus were in German, the settings section was entirely in English. I reinstalled it with the same result.
Win 8.1 x64
system language is German
latest available PAF platform with German as the GUI's language
Apache OO 4.1.1 standard package
no previous version of Apache OO was installed