Should I use t() in a hook_menu's description?
See Strings at well-known places: built-in menus, permissions, log messages and .info files community documentation: 


  The Drupal 6 and 7 menu system stores menu item titles and descriptions in English. This allows the system to cache the data, but display to users using various languages on demand. For this to work, you should not use t() on the title or description of menu items in your hook_menu() implementation. Additionally, you should attempt to use a literal string (rather than a dynamic string) for these two keys, so the translation template extractor can find the string you used.


Emphasis mine.