How to fix ?noredirect=sv_SE links?

The extra parameter is used to set a cookie that prevents the user from being redirect in the future. You have very likely a rel=canonical meta element on the target site that tells search engines the regular URL, so there are no negative side effects.

Is there anything I can do about this though as I think it looks pretty ugly? https://testisivuja.online/en/?noredirect=en_US would look much better if it was just /en instead of all that extra.

You can remove that parameter with the following code. But then disable the automatic redirection, or some of your users will end in a redirect loop.

add_filter( 'mlp_linked_element_link', function( $url ) {
	return remove_query_arg( 'noredirect', $url );
}, 11 );

One last question though, where do I enter this code? In the plugin editor?

You should put it into a separate plugin. See Where do I put the code snippets I found here or somewhere else on the web?

Absolutely fantastic support! Extremely happy with the guidance and assistance you have provided me with! This fixed my issue.