Connect supports different languages in SAP. Specifically, messages and other localized text will be returned in the default language of the user whose account credentials are used to make the call (assuming setup in the SAP system). Data values are not translated.
The ability to specify a language on each call (ex. when using service account but wanting to change languages) is scheduled to be in Connect 1.4 (scheduled for around August 2021). It will work by adding a language parameter as a header to the request.
In the meantime, the workaround would be multiple service accounts – each with their own language – and using the one that ties to the language you want for the request.