One of the default utilities missing from LibreOffice Writer in Ubuntu is a grammar checker, but here is how you can install the LanguageTool plug-in for LibreOffice Writer.
LanguageTool is a style and grammar proofreading software for English, French, German, Polish, Dutch, Romanian, and a lot of other languages. You can think of LanguageTool as a software to detect errors that a simple spell checker cannot detect, e.g. mixing up there/their, no/now etc. It can also detect some grammar mistakes. It does not include spell checking.
LanguageTool Plug-in for LibreOffice (right-click and Save Link As):
Here is more information on how to use LanguageTool:
Make sure you have Java enabled in LibreOffice:
sudo apt-get install libreoffice-java-common
How to install LanguageTool plug-in for LibreOffice:
Open Libreoffice Writer and select Tools and then celect Extension Manager:
Click on ‘Add’ and locate LanguageTool-1.5.oxt that you just downloaded to add it.
Make sure to completely close out of LibreOffice and any instances of LibreOffice running on your system. Restart LibreOffice Writer to test that it has installed sucessfully.