Comment 6 for bug 1024886

What exactly is missing? libreoffice-l10n-sl clearly states: "Spelling dictionaries, hyphenation patterns, thesauri and help are not included in this package. There are some available in separate packages (myspell-*, hyphen-*, mythes-*, libreoffice-help-*)". see: https://launchpad.net/ubuntu/trusty/+package/libreoffice-l10n-sl

Also the package already suggests as such:
Suggests: hunspell-dictionary-sl | myspell-dictionary-sl,
          hyphen-sl,
          libreoffice-grammarcheck-sl,
          libreoffice-help-sl,
          mythes-sl