Long story short, the long descriptions were removed from the core Packages files, no doubt to lower their file-size. Localised descriptions are shipped out in separate files and the main packages list only has a skimpy version, like:
Description: terminal-based package manager
But I'm British (en-GB) so when apt-get update happens, you can see it downloading translations for both US English and GB English:
Hit http://archive.ubuntu.com trusty-proposed/main Translation-en
Hit http://archive.ubuntu.com trusty-proposed/main Translation-en_GB
Both of these files have a separate localised version of the long description but the British trumps that colonial gobbledygook, so when I run apt-cache show aptitude on 14.04, I see:
Description-en_GB: terminal-based package manager
aptitude is a package manager with a number of useful features, including:
a mutt-like syntax for matching packages in a flexible manner, dselect-
like persistence of user actions, the ability to retrieve and display the
Debian changelog of most packages, and a command-line mode similar to that
of apt-get.
.
aptitude is also Y2K-compliant, non-fattening, naturally cleansing, and
housebroken.
That you're not seeing translations suggests that your language has no translation so it's just using the default one-liner from the main Packages list.
You can see a list of available translations in the relevant i18n directory listing. Have a look at yours. Confirm the missing translation and then do... Something. I'm honestly not sure what the process is for adding a new package translation.
Or as muru suggests, you may have disabled translations. Even if you haven't you could hack that to download en translations, even if you aren't English (as long as you can read it!)
