test.rb

# encoding: shift_jis

require 'yaml'

hello = "こんにちは！"
string = "--- #{hello}"

# psych 1.2.2 で例外発生するけど、ruby trunk は例外発生しない:
loaded = YAML.load string

# これで psych 1.2.2 を使える：
loaded = YAML.load string.encode('UTF-8')

p loaded.encoding # => Encoding:UTF-8
p loaded == hello # => false

Encoding.default_internal = Encoding::SHIFT_JIS

loaded = YAML.load string
p loaded.encoding # => Encoding:Shift_JIS
p loaded == hello # => true