Due to their default behavior to handle differences on a line-by-line level most of the version control systems seem to be impractical when writing texts others than source code. Also git highlights changes to text files line-wise.
After some research I found some nice options to improve things.
Coloring words using git diff
git diff --color-words
Coloring words using gitk
gitk --word-diff=plain gitk --word-diff=porcelain gitk --word-diff=color
The gitk parameter option seems to be new and/or undocumented since I could neither find it on the man page of gitk nor I did get it with the auto-completion. Please find further interesting thoughts in the discussion of András Salamon on StackExchange and Eduardo’s post. Also Iain Murray’s cwdiff wrapper might be worth taking a closer look.