sorting world: represent values as letters so that they don't get mixed with indexes

Thx Jean-Marc for noticing.
regenerate the engine l10n; only line positions changed, no manual change
Release 2.2.4: SortingWorld also needs polishing

  * Disable the "help me" button if the appengine is disabled
  * Document the existing colors in Buggle&Turtle worlds
  * Update "About world" dialog's title changed on Human lang switches
  * Change buggle.setColor to setBodyColor so that people used to logo
    don't use it  to change the brush color.
  * Compare turtle worlds with an upsilon to avoid false negatives.
  * Fix an error in the pseudocode of CombSort
  * Fix a bunch of typos in the French translations.
  * sorting world: represent values as letters so that they don't get
    mixed with indexes.