I want to hire a reviewer. I check https://wpml.org/translation-reviewer/ and find the reviewer for some specific language pair, such as Chinese(Simplified) to French, does not exist at all. In such a case, do you have any other sites that can offer professional reviewers?
I can understand your concern. If you're unable to locate a translator proficient in your desired language pair, then it will be better if you could search for a professional from the contractor panel of WPML. There is a category dedicated to the Translation service and I hope you'll get the translation review service from there.
