As a research platform, I guess RG may not disallow researchers to publicize an upcoming conference to seek participation. You may also try to send your ad to the Linguist List, which displays hundreds of them daily.
Yes, you can introduce an international scientific conference on ResearchGate and recommend that researchers participate. To do so:
1. Crete a project / Question or any form you think is easier on RG and then add the relevant keywords and terms as well. provide the website and registration links.
2. Then use the "share" button at the bottom to invite the potential participants on RG.
Here is one example I found on Researchgate. you can consider it.