GuestLog in

This is one of the most complete translation toolsets out there, save for the Shenmue Translation Tools. Most of the work is done for you, but beware: there are still quite a few things you have to implement yourself, like another font (if your language has special characters), and I've found the tool to implement the accents a little spotty.

There is a written guide bundled together with the tools, but you'll soon find out that it doesn't cover a few cases, and you may need help from Terminus themselves, or find a solution on your own. That said, the bulk of the work (extracting/inserting) is already done for you, so this is the go-to tool if you want to start a translation.