Suggested feature: Translations and "closure" post in Spanish

[nikosantis]

I love this project.
As I am interested that more people can read this and continue learning, I would like to make the contribution of adding different translations.

I have added first a copy of the get-posts.js function called get-posts-multilang.js, which receives a "lang" argument, which is a string that would be the ISO code of each language. In this case, as the first translation language I have used "es" (Spanish).
Example: getPostsMultilang('es')

Second, I have added a new route: /pages/[slug]/es.js
At the same time, I've created a folder inside the posts folder called/es, where I've added the post closure in Spanish.
In the /pages/[slug]/es.js path in the getStaticProps function i added more props lang and langList, which will be used in a component similar to "overreacted.io" from the available translations.

Something similar on the original route /pages/[slug].js for the same reason mentioned above.

Finally, I want to mention that I didn't want to add the language path to the beginning of the "concept" (.is/es/[slug]), why?
Because it would break the beauty of the Domain used and the concept of the blog. (whatthefuck.is/[slug])..... (whatthefuck.is/es/[slug]) ... (whatthefuck.is/pt/[slug])
No!
(whatthefuck.is/[slug]/es)... (whatthefuck.is/[slug]/pt) etc.

That would be my contribution.
I hope it is useful.
I intend to continue translating the other posts, if this PR is approved.

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