Thanks to IKVM you can easily turn LanguageTool into a .NET exe or dll (without the GUI and the LibreOffice/OpenOffice.org integration). You will need a fairly recent version of IKVM that uses OpenJDK to make it work.
Just adapt these commands to you local path names (this example shows using mono):
mono /path/to/ikvm/bin/ikvmc.exe -target:library -r:/path/to/ikvm/bin/IKVM.OpenJDK.Core.dll libs/###morfologik.lib###
mono /path/to/ikvm/bin/ikvmc.exe -target:library -r:/path/to/ikvm/bin/IKVM.OpenJDK.Core.dll libs/jWordSplitter.jar
mono /path/to/ikvm/bin/ikvmc.exe -r:/path/to/ikvm/bin/IKVM.OpenJDK.Core.dll -r:###morfologik.lib### -r:jWordSplitter.dll LanguageTool.jar
However, the resulting LanguageTool.exe has not been tested much yet. You should expect problems with resource loading (path names are not recognized properly).
Also see How to add reference to resource folder when generating dll file using IKVM on stackoverflow.com and this forum post.
You can also check if the IKVM can run LanguageTool as runtime (but it could not when we last checked):
$ikvm -jar languagetool.jar