Trick is to convert document into text files and make diff on it.
sudo apt-get install odt2txt docx2txt git config --global diff.odf.textconv "odt2txt" git config --global diff.word.textconv "docx2txt"
Create file ~/.config/git/attributes
and put following lines into it:
*.ods diff=odf *.odt diff=odf *.odp diff=odf *.docx diff=word
Test if it working. Go to your git repository working copy:
git log -p some_document.odt
Instead of
Binary files a/some_document.odt and b/some_document.odt differ
you should see normal text diff.