DPD allows you to set the default language to be displayed in your cart. This setting only affects non-customized text so if you've added any extra text to your DPD pages via the Theme editor you will need to manually translate that there.
Here is a list of DPDs supported languages:
Dansk
Deutsch
English
Español
Français
Italiano
Japanese 日本語
български език
Hrvatski Jezik
Čeština
Nederlands
Eesti
Suomi
ελληνικά
Magyar
Gaeilge
Latviešu Valoda
Lietuvių Kalba
Malti
Język Polski
Português
Limba Română
Slovenčina
Slovenščina
Svenska
Türkçe
To select the default language for your cart click Settings, then Store Setup in the left menu of your DPD dashboard and you'll find the Default Language field in the first block of fields as shown in the screenshot below:
Once you've selected your default language be sure to save at the top or bottom of the page to have this change apply.
Your customers will also be able to select the cart language during checkout using the dropdown list shown below: