You can check if a PO file is valid with the following command:

        msgfmt -c -o /dev/null <po file>
      

The following errors were found in grub2 's PO files:

gettext: po/exclude.pot:1520: duplicate message definition...
po/exclude.pot:1477: ...this is the location of the first definition
po/exclude.pot:2578: duplicate message definition...
po/exclude.pot:2547: ...this is the location of the first definition
po/exclude.pot:2582: duplicate message definition...
po/exclude.pot:2551: ...this is the location of the first definition
po/exclude.pot:2586: duplicate message definition...
po/exclude.pot:2555: ...this is the location of the first definition
po/exclude.pot:2590: duplicate message definition...
po/exclude.pot:2559: ...this is the location of the first definition
po/exclude.pot:2594: duplicate message definition...
po/exclude.pot:2563: ...this is the location of the first definition
po/exclude.pot:2598: duplicate message definition...
po/exclude.pot:2567: ...this is the location of the first definition
po/exclude.pot:2602: duplicate message definition...
po/exclude.pot:2571: ...this is the location of the first definition
po/exclude.pot:2606: duplicate message definition...
po/exclude.pot:2575: ...this is the location of the first definition
po/exclude.pot:4065: duplicate message definition...
po/exclude.pot:1128: ...this is the location of the first definition
po/exclude.pot:4085: duplicate message definition...
po/exclude.pot:1477: ...this is the location of the first definition
po/exclude.pot:4932: duplicate message definition...
po/exclude.pot:4900: ...this is the location of the first definition
po/exclude.pot:4937: duplicate message definition...
po/exclude.pot:4905: ...this is the location of the first definition
po/exclude.pot:4941: duplicate message definition...
po/exclude.pot:4909: ...this is the location of the first definition
po/exclude.pot:4946: duplicate message definition...
po/exclude.pot:4914: ...this is the location of the first definition
po/exclude.pot:4950: duplicate message definition...
po/exclude.pot:4918: ...this is the location of the first definition
po/exclude.pot:4955: duplicate message definition...
po/exclude.pot:4923: ...this is the location of the first definition
po/exclude.pot:4960: duplicate message definition...
po/exclude.pot:4928: ...this is the location of the first definition
po/exclude.pot:7151: duplicate message definition...
po/exclude.pot:1128: ...this is the location of the first definition
po/exclude.pot:7155: duplicate message definition...
po/exclude.pot:4762: ...this is the location of the first definition
po/exclude.pot:7161: duplicate message definition...
po/exclude.pot:1477: ...this is the location of the first definition
po/exclude.pot:7271: duplicate message definition...
po/exclude.pot:1626: ...this is the location of the first definition
po/exclude.pot:7275: duplicate message definition...
po/exclude.pot:1622: ...this is the location of the first definition
po/exclude.pot:7279: duplicate message definition...
po/exclude.pot:4517: ...this is the location of the first definition
po/exclude.pot:7452: end-of-line within string
msgfmt: too many errors, aborting
      

Please ask the translator (identified by the Last-Translator field in the PO file), the language team (identified by the Language-Team field) or debian-i18n for a fix.