Internships could be defined loosely. You could, theoretically, after wwoofing around a bit and taking a pdc, find the specific
project or farm you have been looking for (via whatever channels you have, word of mouth, internet, whatever). You just stay planted there try to make your presence there more official and more "designed". You work more, they give you more responsibility and some sort of title, and you "intern". The world post-pdc is sort of a wild west right now and although there are attempts to create structured post-grad standards in most countries, on-the-ground experience with a good project that values your input and promotes your desires to become a project/farm manager, perhaps even finding you work after you finish, has its merits. Having real experience could, in some cases, be worth more than any post-pdc title you might have. All of this is free, for the most part.
Originally after a pdc, a person would be capable of doing a 2 year internship under someone who was doing permaculture. This was all un-official and the diploma wasn't really the point. The point is 2 years of worthwhile experience. Making sure it is worth your time is where your research comes into play.
Personally, I could have been spending the last year following a post-pdc Diploma in permaculture. That would have been nice, and there's even a diploma-granting body I'm in contact with. I'm not certain that if it was rushed it would be worth having. More importantly, I've used the past year making major steps toward designing and building the system I want, diploma or no diploma. There's good things and bad things about that choice too.
In the end there are choices to be made and consequences to bear. You do your best to make the right ones and bear the weight of not having made others.
All the best,
William