Hello Daniel,
When adding new language to your site, you do not need to define your structure once again. The structure remains the same, the only thing you need to do is to define that you will have more than one langauge for your page and add content for the new language (note that the rad controls are filling automatically for each language). To do so, after you add your language and go to edit mode, click the Manage pages icon. Choose a page for which you want to add a content with the new language and click "Edit". From the dropdown Language list, select the language in which you want to add content and check the checkbox. Note that you must define page name and alias, too.
Click "Go To" and fill your page with content for the langauge you have selected.
Hopefully Sitefinity 2.6 will be released by the end of the week.
Hope this is helpful. If there is any misunderstanding or problem, feel free to write back.
Have a nice day,
Vassil Daskalov
the
telerik team