TYPO3 Core

This is indeed strange, as it seems to work in my installations. Potential causes might be:

- Some extension installed in particular sites which XCLASS some fundamental TYPO3 core class and "breaks" it (check by uninstalling the extensions one by one, until it "works")

- If the "multi-domain" issue is indeed the cause of the problem, it might be interesting for us to know in which exact situation do you see the error and what do you call "multi-domain" exactly (please give an example setup and a "how to reproduce" information).

What I call multi-domain is an install with n sites in the same database, each site root page having a domain record associated.
Strangely, it works now in this installation.

I have another installation, with several sites, each one having its own database, sharing the same sources.
For 1 site, it bugs in the media content, showing what there's in the screenshot I've attached (when I click to add parameters or custom parameters).
For another one, it works with the media content but it produces the error in a FCE in which it's possible to add sections.

After checking extensions in each site and trying to uninstall some, I still have the problem.

The problem only happens in sites which are not running with UTF-8 (not "forceCharset=utf8"). The french backend is rendered in charset=iso-8859-1. This used to work well with "unescape()". The fix from #28952 added the decodeURIComponent() call. Fix #28952 will remove the (superfluous) unescape(). But this will only solve it for UTF-8 backends.

For non-UTF-8 backends I have currently no idea on how to solve this. In my quick research I stumbled over this resource:

http://xkr.us/articles/javascript/encode-compare/

As we want to still support non-UTF-8 charsets in 4.5 LTS, we should try to find a solution that works well in both situations.

For your particular situation, you might consider converting your database and site to UTF-8, which is recommended anyway.