Depends. Can I change the language if I buy a physical copy of the game? If it's possible, I will use English. If it's not possible, I will use German.
You're prevented from changing the language from your local language to english only *IF* Steam states that the game is unavailable for your country [see http://img508.imageshack.us/img508/9581/fdsfdssdaf.jpg] *AND* your physical copy comes from an authorized local distributor which hasn't provided a way to change the game language, such as 1C for Russia, which is going to sell a localized copy of the game which language can't be changed by any means. See http://www.gamesas.com/index.php?/topic/1231316-skyrim-region-block-in-russia-steam/
In short:
- if in your country you can buy Skyrim within Steam you'll be able to change the game language, whether you're going to buy the physical copy of the game at your favorite store or its digital copy within Steam
- if in your country you can't buy Skyrim within Steam you'll be able to change the game language only if the local distributor has provided a way to do it
On a side note, people who can't buy Skyrim within Steam in their countries are
strongly encouraged to NOT buy a physical copy of the game from an online retailer from another country, as they might be unable to activate it due to Steam using region locking [see http://upload.wikimedia.org/wikipedia/en/0/09/Steam_regional_limitation.PNG]. Refer to the http://www.gamesas.com/index.php?/topic/1241932-unofficial-steamdrm-discussion/ for further information.