This tool can merge two templates to become a translation file. It looks at the comments in each template to find out, which msgids belong together.

This is the help screen that appears when you run the tool with no parameters:

msgmergePOT 1.1.1

msgmergePOT usage:
  msgmergePOT english.po otherlanguage.po destination.po

This will create a po file from two identical po extracts that
only differ by the language, for instance the German and English
runtime source code from Borland.