To find messages which haven't been translated to your language yet, this page contains a list of missing and not translated messages which is always up to date.
Then attach the translation here. You will be given credit for your work of course.
A great tool to validate your translation was contributed by Gussi and is located at http://gussi.is/pms/index.php
Gussi wrote:While I was at it I also made a little translation validation tool if anyone is interested: http://gussi.is/pms/index.php - It checks if there are any strings identical to the english translation, also if some are missing or unknown, and if there are any unescaped ! and #. Since the media server will change constantly over time it might be a hassle to update translations, this will hopefully ease the pain for now
If your languages contains any special characters not used in English you will need to use the following tool to save the file:
Languages currently included (some of these will only show up in the next version):
I'll keep this list updated as new languages are added.