So in order to install further features to your LibreOffice installation, like spell checking, dictionary, localization and some other features, in a a very easy way, just copy these simple commands. Mind you that the tag after the package name, refers to my personal taste/installation, i.e.: libreoffice-l10n-pt where pt is my country localization files. in myspell-pt-pt pt-pt is specific to European Portuguese. To get a full list of options and choose your own check the Debian Package page.
To have a better understanding of your code please check this link.
$ sudo apt install myspell-pt-pt hyphen-pt-pt \ libreoffice-l10n-pt mythes-pt-pt libreoffice-help-pt \ aspell-pt-pt aspell-pt
For further info on how to buff up your LibreOffice installation, check Debian Wiki.