META Name Language
To explain in which language your website is in, You use the so called LANGUAGE tag.
The meta tag language declares to users the natural language of the document being indexed. Search engines which index websites based on language often read this tag to determine which language(s) is supported.
This tag is particularly useful for non-english and multiple language websites.
This meta tag has almost no influence on your search engine ranking.
You may add this Langauge meta tag to all of your webpages, so not only in the first index page. Make sure that on every page relevant meta tags are added.