Comment 56 for bug 114375

(In reply to comment #21)
Parts of the English dictionary extension are separated in different Ubuntu packages, but it seems, platform-independent grammar checking component of the original LibreOffice dictionary extension hasn't been supported in Ubuntu, yet.
Debian has got a single grammar checker package here: http://packages.debian.org/sid/libreoffice-lightproof-en, perhaps it works with Ubuntu, too. (If not, try this oxt LibreOffice extension: http://numbertext.org/tmp/lightproof_en-0.4.2.oxt)