Changing general text/add languages

[dammyg]

Hi, I am trying to make a Japanese based site, and I only have the English pack installed.
I have started editing what I can into Japanese, but there are many fields that I am having difficult finding where to edit.
For example the submit-an-article page, log-in page, and much more.
I want to have all this in Japanese, preferably my translation.

If there is already a Japanese language pack, please could you link me to it.
If there is a way to create and add your own language pack, please could you link me to further information.
If there is an area to edit general text like stated above, please could you tell me where to locate it.

Thanks in advance!