OpenCms uses the locale-property of a resource to know in which language the content should be displayed.
To take advantage of this, you can create your content in a folder /en/ (e.g. /en/page1.html /en/about.html) and set the locale-property of the /en/ folder to "en".
You should add content in the other language as well.
To finalize the multi-language setup, you copy the folder /en/ to /de/
Make sure to chose "Copy no resource, just create siblings of all resources in the folder".
Then you set the locale-property of the /de/ folder to "de".
This way OpenCms knows in which language the content must be served.
When you create a new file (in any of /de/ or /en/) do not forget to copy it as sibling to the other folder.