How to translate only the website's interface, not the content?

hi,

I'm building a website with drupal for a german audience. All information on this page will be written in German.

I've started developing the website with the default drupal installation package which comes with English as preinstalled language. I did this because it makes it easier for me to search for solution while developing the site. The biggest part of the drupal community speaks English (I guess), so for example tutorials about how to install something are mostly written in English.

My idea was to develope the site with an english drupal interface and later install the german language package to have the interface translated into German. With "interface" I mean things like labels of submit buttons, field descriptions, etc (basically everyhting except the actual "content" generated by users - for example blog entries).

I'm using the path auto module as welll as the url aliases module to have nicer urls (node/123 -> content/my-first-blog). I wrote a bunch of blog nodes to test the site. With the english language package set to be the default language (admin/settings/language) all nodes urls are perfectly redirected to their corresponding url aliases. As soon as I set German to be the default language all nodes are no more redirected to their url aliases (node/123 stays like this). Whe I try to type in the alias (replacing node/123 with content/my-first-blog in the browser's address bar) I get a "Page not found" error message?!

Also, when I edit a node and save it the url alias is still not working (German is still set as default language).

My questions are:

• Why do url aliases break when I install a new language to translate the website's interface?
• Does installing a new language package mean that there needs to be a translated version of a node in order to be accessible when switching the default language? So for each language there will be a new node stored to the database?
• When I create a new node after I've set German to be the default language, the url alias works. Why?

I don't need translated versions of nodes because when this site goes online, there will be content only in German. All I need is the website's interface translated to German.

How can I keep url aliases working regardless of which language is set as default?

Thanks for any help :)

Best regards.