Change the register button in Event Espresso 3 to say buy tickets.

new_gist_file.php

<?php
//* Do NOT include the opening php tag
 
function ee_replace_register_test_buy_tickets( $translated, $original, $domain ) {
    $strings = array(
        'Register' => 'Buy Tickets',
    );

    if ( isset( $strings[$original] ) ) {
        $translations = get_translations_for_domain( $domain );
        $translated = $translations->translate( $strings[$original] );
    }
 
    return $translated;
}
 
add_filter( 'gettext', 'ee_replace_register_test_buy_tickets', 10, 3 );

References:

https://eventespresso.com/topic/change-text-of-the-register-button-on-events-registration-page/
https://eventespresso.com/topic/change-text-of-the-register-button/
http://eventespresso.com/topic/edit-register-now-text-in-ee3-event-espresso-3-1-37-4-p/
http://eventespresso.com/topic/registration-submit-button-change-text/