For concatenating
Download gettext-0.14.4.exe from http://svn.softwarepublico.gov.br/trac/invesalius/browser/invesalius2/branches/slice_editor/req/gettext-0.14.4.exe?rev=2038
After installing it go to the path "C:\Program Files (x86)\GnuWin32\bin" in command prompt. then use the command msgcat "" "" --output-file="". After it I could concatenate the two po files successfully.