A few years ago I would have confidently and naievely answered no to that question. Unfortunately recently a few scandals made it to the national news that Dutch mental institutions are not in the state we'd like to believe they are. As far as I understand the 'average' mental health patient is treated O.K., but there's not enough budget for the really hard cases where one patient basically requires full time supervision. One scandal was that instead of dealing with a patient like this, the staff had just put him in solitary confinement. Another scandal revealed cases of bullying and sexual abuse by staff. The sort you'd expect in a big organization with humans and awkward power relations, I can't say for sure if it's any better than those in the US.

> solitary confinement is a distinctive US problem

Not really, it's a problem in Europe too. We just don't talk about it.

If you get arrested here in Finland, you'll by default be in solitary and will remain so until the cops, not the courts, feel like letting you out.

Has anyone tried to challenge that sort of thing in the European Court of Human Rights?

Yes, and Finland for example has consistently lost. The problem is that in practice these court decisions only end up benefiting the individuals bringing the suits, as it's almost impossible for public workers to get fired here they can safely ignore those decisions in most cases.