incorrect hyphen and capitalization

Hi Ruben,
I wonder if you could fix an issue in your your plugin.
according to IANA (https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry) and https://tools.ietf.org/html/rfc5646 references the language should be written in lowercase and using a hyphen
Example:
<link rel=”alternate” href=”https://google.com/&#8221; hreflang=”en-us” /> USA
<link rel=”alternate” href=”https://google.com/&#8221; hreflang=”en-gb” /> UK

At the moment is generating
<link rel=”alternate” hreflang=”en_US” href”https://google.com&#8221; /> USA
Could you fix it so it pass the w3c validation?

Hope that helps.

Regards

Luis Gellon

https://www.ads-software.com/plugins/language-selector-related/