Moving this discussion to the Adobe Digital Editions forum.
The User Interface language for Adobe Digital Editions 1.7.2 and later including Adobe Digital Editions 2.0 is affected by the language setting of your operating system. Please be aware that the User Interface does not affect the content which you wish to view. If you wish to open a Dutch ePub/eBook you would be able to do so.
If you wish to adjust the language of Adobe Digital Editions then please uninstall, adjust the language for your Operating System, and then reinstall.
Finally in regards to transferring content to your Kobo device please see Transfer eBook to eReader | Adobe Digital Editions - http://helpx.adobe.com/digital-editions/kb/transfer-ebook-ereader-digi tal-editions.html.