Here you go. There's a patch for lang_en.inc.php and one for serendipity_event_multilingual.php, and a short documentation text in documentation_en.html. Both patch files are diffs against the files currently available through Spartacus.

I'm not sure I conform entirely to conventions. For instance ...

Thanks. There we go. Stuff works.
Strangely, the date localization issue fixed itself magically somehow. I'm not entirely sure how that happen, it just started working suddenly, while I was fixing the entry title processing :)
I'm guessing it could be because the server finally registered the new ...

There we go. RSS feeds and sidebar items are translated. Escaping the brackets will exclude them from the processing. You can see the result here: http://struntprat.dk
There are still two quirks I haven't been able to work out, though:

1. Date name translations (in the archive sidebar item, for ...

Ah. Thanks for the tip. I'm not entirely sure how I overlooked the rss hooks, and I will take a look at enabling escaping. Maybe I can work it all out somehow, anyway, even if I am a bit lazy. :)
Newlines to br conversion is enabled for entries by default in the plugin Markup: NL2BR, which is ...

Great! Thanks.
I think I'll start by trying the latest Subversion checkout of Serendipity. If that turns out to be broken in some way, I'll make do with the template hack, for now. :)

Right now, it's just a very small plugin at 45 lines with no configuration options. And I rely on the Language ...

Well, I wanted to try and make a simpler plugin for multilingual entries, by using tags instead of storing translations separately in the database.
So an english/danish/swedish entry might look like this in the database (don't mind the weird-looking tags. It's what I came up with at the time ...

Hi, I was wondering if there is any information on this apparently missing hook. It is listed as an event hook in the Plugin API: http://www.s9y.org/116.html
But it does not appear to exist anywhere in the code. Unfortunately, that list is from 1.0-alpha1, so I guess the hook may have disappeared ...