According to my understanding, ResearchGate is specifically designed for researchers to share their work and collaborate with others in the academic community. As a result, I believe you can upload an English translation of your book or article to ResearchGate even if it was originally published in another language.
See the help page "How to add research" (https://help.researchgate.net/hc/en-us/articles/14293005132305): "You can add all kinds of work to ResearchGate, such as conference papers, preprints, or even negative results." I used the type "data" when I uploaded unpublished English translations of some of my papers and book reviews, see https://www.researchgate.net/publication/366985534 as an example.