Common questions
How do I remove the link to the other translation at the bottom of my page ?
You can do this from the Multilingual setup page: admin/settings/language/i18n
Select "Hide content translation links".
I started a site with English as the default. How do I change it to German?
What I would like to do is to have English nodes come up with example.com/en, and the German nodes with plain example.com.
Edit the path prefix for each language. Go to admin/settings/language and edit each language. Set the path prefix for English to en and the path prefix for German to "empty".

Comments
RTL?LTR
Now i have a tow language site in drupal cms ,i want to set the menue in rtl system when visitors select the language switch button , how i can do this ?
You need to modify your theme
You need to modify your theme to have your menu displayed RTL for RTL languages. You should create a style-rtl.css file in your theme for this.
The default garland theme shows how to do this.