Florian,
you need to do some research on a topic called character encoding / character decoding.

I'll give you some hints, which will get you going:
If I type something here, my editor or browser has set a character encoding. Lets say utf-8. Now you store it to your database. Most people do not know, which character encoding there database is actually using. MySQL for example uses latin 1 per default. So it could be that your transmitted data is stored in latin 1 instead of your original encoding. Next step is when you want to pick up the data again from your database to display it somewhere. It could be that your database delievers the data in a different encoding than it uses to store it... Not to mention the client i. e. webbrowser, which will show it up again. Do you know, it is using utf-8, latin1 or whatever to show what it has got to display?

You can only solve this, if you know exactly what is going on and where it is happening. Every step can be configured or manipulated. Google provides a lot of stuff on that issue.

Hope this helps.

one other thing to check is if your ss templates are encoded in utf-8. its usually a setting in the authoring software (notepad++, dreamweaver, whatever you are using). I know that makes a difference for the translated static text stored in the lookup tables like mysite/lang/en_US.php, but not sure if it makes a difference with content from the database. its normal to see the translated umlauts in the database.

hope it helps,

-Chris