The command line tool msgmerge is used to merge translated strings from two PO files into one. It is really easy to use, here is an example:

msgmerge updated-po-file reference-file > output.po

The result in output.po contains the reference-file with the new translated strings from the updated-po-file.

This tool can be used to merge strings from a stable branch into the development branch (or vice versa).

An example is probably handy. Suppose you have a Dutch translation file for a package called “packageW”.

This is fully translated in the stable “Xfce 4.8” and needs to be merged with an incomplete Dutch translation file in the development branch “master”. Goal: prevent unnecessary work in translating the development branch.

Both files are in the directory Downloads of your home directory, which is the usual location of downloaded files.

Copy/paste the following command in your terminal:

cd Downloads

(press Enter)

Now copy/paste the following command in your terminal:

msgmerge packageW-xfce-4-8.nl.po packageW-master.nl.po > NEWpackageW-master.nl.po

(press Enter)

Then delete both “packageW-xfce-4-8.nl.po” (you don't need it anymore) and “packageW-master.nl.po” (you don't want a name conflict in the next step).

Then rename “NEWpackageW-master.nl.po” to “packageW-master.nl.po”.

Finally: upload “packageW-master.nl.po” in Transifex.

Note that you cannot send the output directly to “packageW-master.nl.po”, as it will fail with a totally unchanged PO file (because of the name conflict).