When GNUN detects a file named pot in some po directory, it writes to it all strings from all articles in the same directory; it also merges translations of those strings to files named lang.po, for all languages available in that directory. In its turn, files lang.po are used to update translations in articles from that directory.
This helps updating translations in sets of articles like proprietary/ section, where an item may belong to many files at once. The translator can only update lang.po, or any article where the outdated item is listed. Then GNUN will copy the translation to all other places.