Asi by mohlo fungovat tohle: http://jsfiddle.net/setalosas/mezopfhL/, ale kam přidat ten skript do Fastcentriku?

<iframe id="existing-iframe"
width="640" height="360"
src="https://www.youtube.com/embed/q2C0EO0zzAY?enablejsapi=1&cc_load_policy=1"
frameborder="0"
style="border: solid 4px #37474F"
></iframe>

<script type="text/javascript">
var tag = document.createElement('script');
tag.src = 'https://www.youtube.com/iframe_api';
var firstScriptTag = document.getElementsByTagName('script')[0];
firstScriptTag.parentNode.insertBefore(tag, firstScriptTag);

let player

const onApiChange = _ => {
if (typeof player.setOption === 'function') {
player.setOption('captions', 'track', {languageCode: 'en'}) // undocumented call
}
}

function onYouTubeIframeAPIReady() {
player = new YT.Player('existing-iframe', {events: {onApiChange}})
}
</script>