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:4073: duplicate message definition...
po/exclude.pot:1128: ...this is the location of the first definition
po/exclude.pot:4093: duplicate message definition...
po/exclude.pot:1477: ...this is the location of the first definition
po/exclude.pot:4940: duplicate message definition...
po/exclude.pot:4908: ...this is the location of the first definition
po/exclude.pot:4945: duplicate message definition...
po/exclude.pot:4913: ...this is the location of the first definition
po/exclude.pot:4949: duplicate message definition...
po/exclude.pot:4917: ...this is the location of the first definition
po/exclude.pot:4954: duplicate message definition...
po/exclude.pot:4922: ...this is the location of the first definition
po/exclude.pot:4958: duplicate message definition...
po/exclude.pot:4926: ...this is the location of the first definition
po/exclude.pot:4963: duplicate message definition...
po/exclude.pot:4931: ...this is the location of the first definition
po/exclude.pot:4968: duplicate message definition...
po/exclude.pot:4936: ...this is the location of the first definition
po/exclude.pot:7159: duplicate message definition...
po/exclude.pot:1128: ...this is the location of the first definition
po/exclude.pot:7163: duplicate message definition...
po/exclude.pot:4770: ...this is the location of the first definition
po/exclude.pot:7169: duplicate message definition...
po/exclude.pot:1477: ...this is the location of the first definition
po/exclude.pot:7279: duplicate message definition...
po/exclude.pot:1626: ...this is the location of the first definition
po/exclude.pot:7283: duplicate message definition...
po/exclude.pot:1622: ...this is the location of the first definition
po/exclude.pot:7287: duplicate message definition...
po/exclude.pot:4525: ...this is the location of the first definition
po/exclude.pot:7460: 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.