Why isn't the english language pack available in Origin?

They probably thought that everybody who wants the game in English has the client set to English anyways, which will install the game in that language. If you had the client in German before installing the game you can also switch the client to English, close it, delete the folders loc and locfacefx under Origin Games\Dragon Age Inquisition\Data\Win32, open the client, right click on Inquisition and select "repair". That will download the English voice files.