When starting a new translation, the translator creates a file called LANG.po, as a copy of the package.pot template file with modifications in the initial comments (at the beginning of the file) and in the header entry (the first entry, near the beginning of the file).
The easiest way to do so is by use of the ‘msginit’ program. For example:
$ cd PACKAGE-VERSION $ cd po $ msginit
The alternative way is to do the copy and modifications by hand. To do so, the translator copies package.pot to LANG.po. Then she modifies the initial comments and the header entry of this file.