Most programs are written using American English spelling. It is a simple process to change the spelling to British English to satisfy the eye of English speakers in Canada, Australia, South Africa and other commonwealth English speaking countries.
These are useful references to the difference between the various English spellings.
To initialise all the POT files to be fully translated:
for pot in `cd templates; find . -name "\*.pot"` do mkdir -p en_GB/`dirname $pot` msginit --locale=en_GB --no-translator -i templates/$pot -o en_GB/`dirname $pot`/`basename $pot .pot`.po done
To examine all potential American spellings use pofilter:
pofilter -t musttranslatewords --musttranslatefile=en_US-words-to-change en_GB en_GB-check
If a msgid contains any of the words listed in the files en_US-words-to-change then these will be extracted to en_GB-check. Correct them and then run:
pomerge -i en_GB-check -o en_GB -t en_GB
This will not check for bad grammar, sentence structure, humour, etc. You need a person to do that. But its a start.