Hello, Pawel!
I have no idea of an automated process to transform XML into PO and then
merge that PO with another PO.
You may want to check on the fedora-translator's list; sorry I don't have
the info about it handy.
If you can find how this can be done, please tell us here. Maybe we can
develop a tool to do this.
We can easily originate documentation in any language, it need not be US
English. For example, you could write an original document in Polish, and
set ${PRI_LANG} to "po" in the "Makefile". Later a translator could
add
"en_US" to the "${OTHERS}" macro in the "Makefile" and
produce a
"po/en_US.po" file.
If you do not mind experimenting, you could try using xml2po to generate a
.POT file from your Polish XML. Then, copy the en_US version of the
original document POT file into a "po/pl.po" file. Now, use a visual diff
tool such as "meld" or "mgdif" or "tkdiff" (help me out with
names, gang!)
and update the pl.po file with the English "original" strings. I have not
tried it, so this may be a waste of time.
HTH