f vi and a bash shell are totally foreign to you, jump to that page
whether you are command line (and vi) -friendly:

1. Jailbreak your iPhone, and install the following packages -

1 • BSD Subsystem
2 • Term-vt100
3 • Erica’s Utilities (be certain to edit your path to include /var/root/bin)

2. Fire up the terminal app on your phone and…

cd ~/Library/Preferences
plutil -c xml1 .GlobalPreferences.plist
vi .GlobalPreferences.plist

3. Find the following text:

<array>
<string>en US</string>
</array>
…and edit it to add a line so it looks like that:

<array>
<string>en US</string>
<string>ja</string>
</array>

4. Save and close the Terminal app.

When you visit any application that uses a keyboard now, there will be a globe next to the ‘123’ characters key. Selecting that will alternate amidst your US and Japanese keyboards. The Japanese keyboard is pretty easy to distinguish, considering it is compressed to form room for a kanji/kana suggestion field, and has a expanded hyphen to the right of the ‘L’ key.

–　頑張ってください！

Original post by admin