How do I change change language in the animated countdown ?

if the html lang attribute changes to the new language – the labels are not translated?
does your lang plugin set a html lang attribute?

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anyway:
give a unique ID to your countdown element f.e.: spanish

then follow the exemple here: https://enfold.webers-webdesign.de/3-columns/

for child-theme functions.php:

function set_spanish_translations(){
?>
<script>
window.addEventListener("DOMContentLoaded", function () { 
	(function($) {       
		$('#spanish').attr('lang', 'es-ES');
		$('#spanish .av-countdown-years .av-countdown-time-label').attr({'data-label': 'Año', 'data-label-multi': 'Años'});
		$('#spanish .av-countdown-months .av-countdown-time-label').attr({'data-label': 'Mes','data-label-multi': 'Meses'});
		$('#spanish .av-countdown-weeks .av-countdown-time-label').attr({'data-label': 'Semana','data-label-multi': 'Semanas'});
		$('#spanish .av-countdown-days .av-countdown-time-label').attr({'data-label': 'Día','data-label-multi': 'Días'});
		$('#spanish .av-countdown-hours .av-countdown-time-label').attr({'data-label': 'Hora','data-label-multi': 'Horas'});
		$('#spanish .av-countdown-minutes .av-countdown-time-label').attr({'data-label': 'Minuto','data-label-multi': 'Minutos'});
		$('#spanish .av-countdown-seconds .av-countdown-time-label').attr({'data-label': 'Segundo','data-label-multi': 'Segundos'});
	}(jQuery)); 
});
</script>
<?php
}
add_action('wp_footer', 'set_spanish_translations');

it differs between data-label and data-label-multi – for singular and plural form of the Units