There have been reports of a Notice: Undefined index: icon in wp-content/plugins/multilingual-press/inc/types/Mlp_Translation.php on line 63

This can happen if the config array is missing the 'icon' element.

In Mlp_Language_Api:L326-L340, the 'icon' element is only set when 'http_name' is not empty:

if ( '' !== $data[ 'http_name' ] ) {
        $arr[ 'icon' ] = $this->get_flag_by_language(
            $data[ 'http_name' ],
            $site_id
        );
    }

An easy fix would be to ensure the 'icon' element is set in any case.