Undefined index in mqtranslate_hooks

I am getting this error: Notice: Undefined index: cn in /snip/wp-content/plugins/mqtranslate/mqtranslate_hooks.php on line 57.

Here is my debug info:

Array
(
    [enabled_languages] => Array
        (
            [0] => zh
            [1] => en
            [2] => cn
        )

    [default_language] => zh
    [detect_browser_language] =>
    [hide_untranslated] =>
    [show_displayed_language_prefix] => 1
    [auto_update_mo] => 1
    [hide_default_language] => 1
    [url_mode] => 2
    [language_name] => Array
        (
            [en] => English
            [zh] => 繁體中文
            [cn] => 简体中文
        )

    [locale] => Array
        (
            [en] => en_US
            [zh] => zh_HK
            [cn] => zh_CN
        )

    [not_available] => Array
        (
            [en] => Sorry, this entry is only available in %LANG:, : and %.
            [zh] => 對不起，此內容只有%LANG:, : 和 % 版本。
            [cn] => 对不起，此内容只适用于%LANG:，:和%。
        )

    [mqtranslate_services] =>
    [use_strftime] => 4
    [date_format] => Array
        (
            [en] => %A %B %e%q, %Y
            [zh] =>
            [cn] => %x %A
        )

    [time_format] => Array
        (
            [en] => %I:%M %p
            [zh] =>
            [cn] => %I:%M%p
        )

    [flag] => Array
        (
            [en] => gb.png
            [de] => de.png
            [zh] => hk.png
            [fi] => fi.png
            [fr] => fr.png
            [nl] => nl.png
            [sv] => se.png
            [it] => it.png
            [ro] => ro.png
            [hu] => hu.png
            [ja] => jp.png
            [es] => es.png
            [vi] => vn.png
            [ar] => arle.png
            [pt] => br.png
            [gl] => galego.png
            [pl] => pl.png
            [sr] => rs.png
            [cn] => cn.png
        )

    [flag_location] => plugins/mqtranslate/flags/
    [ignore_file_types] => gif,jpg,jpeg,png,pdf,swf,tif,rar,zip,7z,mpg,divx,mpeg,avi,css,js
    [ul_lang_protection] =>
    [allowed_custom_post_types] => Array
        (
            [0] => video
            [1] => event
            [2] => tab
        )

    [disable_header_css] => 1
    [use_secure_cookie] =>
    [cookie_enabled] => 1
    [language] => en
)

https://wordpress.org/plugins/mqtranslate/