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unidecode library is good enough for transliteration other than asian languages.
But there are so many asian people living and many Japanese and Korean are current user of sites using Drupal.
It will be better to support complex languages such as Japanese and Korean in transliterate module.
Now I'd like to propose you or someone who is interested in to implement unihandecode functionality in transliterate module.
Unihandecode (https://launchpad.net/unihandecode) is a project and a running code that is forked from unidecode to support Japanese, Korean and other languages in Python in addition to original unidecode functionality.