What's the difference between Language Switcher and Translation block?
Key words and phrases
i18n what's the difference between Language switcher Translations blockTags
Description
Deep in this old thread, "Looking for internationalization use cases and application feedback" - http://drupal.org/node/88417 - a user wrote:
I'm not sure what I did wrong but the Language Switcher block failed to work on mine site. I've to use Translation block instead
Good enough for me to start out with Translation as the block, since they look identical anyway...

Now I've looked at the source code and Agaric has proudly posted answers to this on the i18n issue queue-- the code is different, in the call to a translation.module function (translation is a sub-module of i18n and provides the Translation block as an alternate, translation-aware version of the simple language switcher.)
Link when we find it...
Link: http://drupal.org/node/179991