Maybe, for the PC version. The Xbox version has no language options, that I could see, and switches localizations (if available) based on the Xbox language setting (at least for the North American English/French release).
In the main Divinity 2 install folder there is a file called lang.ini which consists of something like:
[general]
Language=EN
LanguageFull=English
In the Data subfolder, the languages.xml file contains something like:
<Languages>
<Language XBox="Default" Spoken="English" Text="English" />
</Languages>
The English version of D2:DC also contains the Italian and Spanish text, so in the lang.ini file the values can be changed to IT/Italian or ES/Spanish and in the languages.xml file the 'Text' value can be changed to Italian or Spanish.
I have not tried installing a non-English version of Divinity 2, but in principle you should be able to copy the language specific files from one install to another (don't know if Steam removes the existing language files if you switch languages). After that, I think changing the value of 'Spoken' to German and the main/text to English should do what you want.
