I have been asked to serve on the examination committee for a PhD thesis. It's in the area of machine learning. It's from a university in a developing country. My job is to provide a written report, recommending whether to award the degree (possibly with minor or major changes), or even not to proceed to defence. I won't be participating in the defence itself.
The quality is very bad. I would say it would receive a low grade, if evaluated as a 3-month MSc dissertation, in my university (in a developed country, but not a top-tier university). It's bad in every respect - novelty, experimental design, understanding, motivation, contact with literature, writing, reliance on "predatory" journals, even some (fairly benign) plagiarism. So, my instinct is to recommend it should not proceed to the defence.
My problem is that standards vary between countries and between institutions. How much allowance should I make for this? I do not want to perpetuate a "vicious cycle" which prevents high-quality work in developing countries (eg Breaking the (perhaps perceived) academic (poverty) cycle).
Part of my problem is that I don't know how much weight my report will carry. Maybe the department is used to receiving harsh reports from international committee members, and de-weights them. Or maybe a harsh report from an international member is enough for an immediate fail.
If I could allocate the blame in my review, I would say the supervisor surely deserves most of it. But it is the student who will suffer the most, if they fail. On the other hand, perhaps the supervisor's own PhD was the beneficiary of some lenient reviewing in the past, leading them not to know what standards are expected. I should not perpetuate that cycle either.
I hope my question does not sound condescending or insulting to scholarship in developing countries. I know that great research is done everywhere, and I have great respect for many individual researchers from the country in question.
Edit: of course, there are no right answers here, but I accepted @anon's answer because the "PhD = passport to worldwide community" concept was the most helpful in my thinking. In the end, I wrote a fully honest review from my point of view, and recommended it should not go to defence, but I added a note that I understand the local committee will apply the institutions' own standards. It goes without saying that I was constructive, not negative, and gave a lot of advice for accessible improvements. Thanks to all for a useful discussion!