Why did the dialogue in skyrim change languages

Copies of Skyrim sold for consoles have limited language options. It seems like it should be possible to install both French and German from the German PS3 copy of Skyrim. Make sure your PS3 is set to German and try reinstalling the game.

If that fails, contact Bethesda customer support, or the retailer where you purchased the game. They should be able to either exchange the disc or tell you how to install the version of the game you need from the disc.

See also: Where are the language settings in the Xbox 360 version of Skyrim?

The DLC are completely independent and compatible with the original game, no matter your game progress or installation order.

Meaning, you should install the game with all updates and DLC, and start playing as you like.

Note that for Hearthfire you will need to complete some standard quests to be able to buy your land. And for Dawnguard you will have to be around level 10.