(D5) Creating a translations block that is aware of node tranlations

I've currently got a Drupal 5.13 site in development that I have set up to use 3 languages using the Internationalisation module (i18n, v5.x-2.4).

My question is about the Translations block, it currently shows all the enabled languages, but I have a request from the client that if the node being viewed is not available in one of the 3 languages it should not show the link to that language.

Here's an example to better explain...

Site has 3 languages: English, French and German

On a page that has all three languages the block at the top of the page should say "English | French | German";
on a page that is currently only available in English and German the block should only say "English | German".

I've spent a day trawling posts and blogs to try and find a solution but to no avail. I'm fairly new to Drupal coding, so my ideal solution is a bit of code I can simply dump in a custom block. Can anyone help, or at least steer me in the right direction?