How to implement a horizontal set of translation links for every node? I want to add a hardcoded translation block to my page.tpl.php, to link to a translated version of every node + a translated interface.

The Language Switcher Dropdown module did the trick, but I want a horizontal set of links and need something simpler.
Maybe Displaying and configuring a drop down using Language Switcher Dropdown helps to achieve what you're trying to do with this module anyhow.

If not then the answers to the question about How to theme language translation links in Drupal? may help to actually answer your qestion. Though that question is for D6, and hence its answers might need some review to also make it work in D7. Here is the relevant part of it that might do the trick:

$node = menu_get_object();
if ($node-&gt;links) {
  print theme('links', $node-&gt;links);
  }