SEO hreflang
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The SEO hreflang module specify the proper hreflang code using the custom language format (e.g., es-es, en-us). <link rel="alternate" hreflang="en" href ="URL" />or <link rel="alternate" hreflang="en-us" href ="URL" />

Add hreflang attribute for SEO purpose in single language site and multilingual as well.

Installation
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1) Download the module and place it inside the modules/contrib directory.