Unable to install LanguageTool 2.5 extension for LibreOffice 4.2 on Ubuntu 14.04

First of all, the most important:

sudo apt-get installlibreoffice-java-commonjava-common

Go to LibreOffice Options menu, choose Advanced and be sure Use Java runtime environment is checked and a Java version is selected.

Now install your extension either by double-clicking on it in File Manager or by importing it in LibreOffice Extension Manager dialog.