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If currently selecting a variant reloads the page does the correct file download?
If so the simplest method is in a custom-lliquid or custom-html section/block to create javascript to just reload the page when the variant changes.
Plenty of posts about that for various themes on the forums refresh reload page variant changes insert themename
Alternatively have different products for different languages and just make the select dropdown send them to the relevant page.
Most themes have javascript event like variantChange or some such or you can listen to the underlying hidden select if it exists for your theme.
Example starting code of functions set for the .single-option-selector element, untested
Using jquery library if that's also in the theme
$('.single-option-selector').on('change', function(){ /*yourlogichere*/ })only javascript
<script>
function yourbusinesslogicfunctionname (){
/* logic when the variant changes */
}
function variant_change_listener(elementSelector, callback){
const selector = elementSelector;
const emitting_element = document.querySelector(selector);
emitting_element.addEventListener('change', function(){
callback ? callback() : console.log("variant changed, but no callback function");
});
}
// either call listening function directly in flow of document or set it to run after document ready
variant_change_listener('.single-option-selector', yourbusinesslogicfunctionname );
</script>
Though some like the latest Dawn theme and it's offshoots use a pubsub event model.
i.e. something like the following keeping in mind metafield data is not part of the ajax json api so the metafields stuff needs to be already in the html or you have to fetch it using the section rendering api
<span id="ELEMENT-ID"></span>
<script type="text/javascript">
const element = document.getElementByID("#ELEMENT-ID")
updateElementSubscriber = subscribe("variant-change", (e)=>{
element.innerHTML = e.data.variant.title
})
</script>
