As Lukáš Lalinský has stated, unicode is a standard, it is not a piece of software that you can install into your computer. However, if you want to develop PHP websites for the Japanese language, you'll have to have an editor which can display Japanese. i.e. an editor which can map unicode characters with the appropriate (Japanese) fonts. Then, if you want to type Japanese, of course you'll need a Japanese IME (input method editor). My personal picks are vim, Eclipse, or Notepad++ if you're using Windows.
As a side note, you may want to have a look of the following settings in php.ini also:
- mbstring.language
- mbstring.internal_encoding
- mbstring.http_input (actually this
should be set to "auto" in general
cases)
- mbstring.http_output
Good luck!