Yes maread01 the files will be contained on your old laptop in the location indicated in message #7. As Sjpt your content is all stored on your local computer. If you made a backup of your documents folder though then you should still have access to your purchased content within your backup.
The user interface for Adobe Digital Editions is determined by your computers Region and Language Control Panel. Please make sure the language is set for Dutch and the user interface should be adjusted.
The user interface though does not influence the language of the content viewable within Adobe Digital Editions. If your content is in Dutch then it will be display in Dutch.