The short version: There is a popular Mexico-based website that has been translating our articles into Spanish sentence-by-sentence, and posting them as their own works. They also take some of our images and artwork without credit. The offending site appears to have a large following (larger than my own site, anyway), with over 100k followers on Facebook.
Long version: I discovered two articles plagiarized in this way because the person posting it had added "Source: [our site name here]" at the bottom of the text, and it triggered a Google alert. Looking around their site I soon found additional articles that were directly translated from our material sentence by sentence, and none of these cited their source.
I emailed the listed contact address, asking them to take down the unauthorized translations (in a polite, professional tone, just in case this was the work of a rogue contributor or something). They did not reply, but they did swiftly edit those two articles to remove the "Source" line from the bottom.
So far I have have found 36 (!) articles on the offending site that are direct translations of our work, going back nine years. There may well be more I have not yet found, they are mixed with many other articles (which are probably plagiarized from other sources).
The site appears to be hosted on Google Cloud Platform. I reported the plagiarism to Google's Cloud Platform abuse department over a week ago, but predictably they have not responded apart from some automatic replies.
I've contacted a few IP attorneys, and that route is looking expensive, and unlikely reach a satisfactory resolution.
Is there anyone here who has dealt with something like this? Any advice?