Clean up whitespace and space-tab-mix.
Ensure a defined localisation environment.

See e.g. the GNU gettext documentation for more details:
http://www.gnu.org/software/gettext/manual/html_node/Locale-Environment-Variables.html
Simplify the "sudo" usage and reduce redundancies.
Use central variables for repeating filenames.
Remove unnecessary quotes.
Give an explicit exit status if we didn't do anything.

And move printing of the usage help into a function.