When you install Ubuntu with some localization only basic translation set is installed as all of the localizations take up too much space on CD. The easiest way to get all localizations is to go to System -> Administration -> Language support. This application informs user that the language support is incomplete and installs missing packages.
If user never checks Language support, he never gets complete localizations and can not experience Ubuntu as fully in his language.
Full set of translations should be downloaded during install of with first update.
Here is package set for Latvian (lv):