Character corruption on commit diff page

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Hello, we are using GitLab 7.13.5 in Japanese language environment,
now we’re facing character corruption problem when viewing commit diff page.

expected: 関連のGameObjectは一部の例外を除き、この階層下に紐付きます。
actual:   髢｢騾｣縺ｮGameObject縺ｯ荳驛ｨ縺ｮ萓句､悶ｒ髯､縺阪√％縺ｮ髫主ｱ､荳九↓邏蝉ｻ倥″縺ｾ縺吶

On prior version 6.8.1 the character corruption was not seen.
After upgrading to 7.13.5, modified some related code in config/application.rb and .gitconfig to be fit Japanese language environment, still the issue appears.

# config/application.rb
module Gitlab
   class Application < Rails::Application
    config.i18n.enforce_available_locales = true
    config.i18n.default_locale = :ja
    config.i18n.locale = :ja

# ~/.gitconfig
[core]
autoCRLF = true
pager = nkf -s | LESSCHARSET=utf-8 less

Thanks in advance for any hint!