Arefly

Disallow Japanese Language Comments in Your Blog. (Full Support with AJAX Comments Too!)
在你的部落格中禁止日文評論（? ?面支持AJAX評論提示）
Live Demo: <a href="http://www.arefly.com/no-japanese-comments/#respond" rel="nofollow ugc">Click Here</a> (Try Enter Some Japanese there)
<h4>Translators</h4>
<ul>
<li>Chinese, Simplified (zh_CN) – <a href="http://www.arefly.com/" rel="nofollow ugc">Arefly</a></li>
<li>Chinese, Traditional (zh_TW) – <a href="http://www.arefly.com" rel="nofollow ugc">Arefly</a></li>
<li>English (en_US) – <a href="http://www.arefly.com" rel="nofollow ugc">Arefly</a></li>
</ul>
If you have created your own language pack, or have an update of an existing one, you can send <a href="https://codex.wordpress.org/Translating_WordPress" rel="nofollow ugc">gettext PO and MO files</a> to <a href="http://www.arefly.com/about/" rel="nofollow ugc">Arefly</a> so that I can bundle it into No Japanese Comments. You can download the latest <a href="https://plugins.svn.wordpress.org/no-japanese-comments/trunk/lang/no-japanese-comments.pot" rel="nofollow ugc">POT file</a>.

No Japanese Comments

Disallow Japanese Language Comments in Your Blog. 在你的部落格中禁止日文評論

Hizbul Bahar

Main feature and goal of this plugin ‘Block Spam Comments’ is to detect spam comments and create a shield to protect from submit this unwanted robot comments without using captcha. Plugin size is less than 1 KB, so no tension about storage size. Install and Activate then enjoy spam free website.

No Japanese Comments vs Block Spam Comments