Currently neither the source, nor the target language or the UI language selected does get reflected in the language that the SmartReview quality ratings are done.

I have asked support and they confirmed that currently the language is always English by design.

This could be a problem in e.g. German to Spanish translation projects if the reviewers looking at the quality assessments does not understand English well enough.

I think it should be configurable as part of the project settings to select the language used for the SmartReview explanations.

(This issue got raised with support as CS0036573) and they suggested to raise an idea...