wecr_bbp_topic_message_global.php

<?php
	/**
	 * Override topic feedback message
	 *
	 * @param string        $translated_text_out    the original feedback text
	 * @param string        $translated_text_in 	The text that bbPress sent in to the function, or the 'default' text bbPres uses here
	 *
	 * @return string       $translated_text_out    the filtered feedback text
	 */
	function custom_topic_feedback_messages( $translated_text_out, $translated_text_in ) {

		switch ( $translated_text_in ) {
			case 'You cannot reply to this topic.': // put your language string here
				$translated_text_out = 'Put in your message going out';
				break;
		}

		return $translated_text_out

	} // topic_feedback_messages
	add_filter( 'wecr_bbp_topic_global_message', 'custom_topic_feedback_messages', 10, 2 );