A first cut implementation of meta tags for alternate languages

reference https://support.google.com/webmasters/answer/189077?hl=en

src/templates/chapter.js

@@ -211,22 +211,40 @@ export default ({
  data: {
  currentPage,
  pages,
- site: { siteMetadata: { title: siteTitle, toc, githubUrl, codeGithubUrl } },
+ site: { siteMetadata: { title: siteTitle, toc, githubUrl, codeGithubUrl, siteUrl } },
  },
  location,
 }) => {
  const entries = tocEntries(toc, pages);
- const { frontmatter: { commit, title, description }, fields: { slug, chapter } } = currentPage;
+ const {
+ frontmatter: { commit, title, description },
+ fields: { slug, chapter, framework, language },
+ } = currentPage;
  const githubFileUrl = `${githubUrl}/blob/master/content/${slug.replace(/\//g, '')}.md`;
 
  const nextEntry = entries[toc.indexOf(chapter) + 1];
 
+ // This is not optimized.
+ let altLangUrl;
+ if (language === 'es') {
+ altLangUrl = 'en';
+ } else if (language === 'en') {
+ altLangUrl = 'es';
+ }
+
  return (
  <DocsWrapper>
  <Helmet
  title={`${title} | ${siteTitle}`}
  meta={[{ name: 'description', content: description }]}
- />
+ >
+ <link
+ // TODO: map every language supported and generate an alt URL for each
+ rel="alternate"
+ hrefLang={altLangUrl}
+ href={`${siteUrl}/${framework}/${altLangUrl}/${chapter}`}
+ />
+ </Helmet>
  <Sidebar>
  <Heading>Table of Contents</Heading>
  <DocsList>
@@ -310,6 +328,8 @@ export const query = graphql`
  fields {
  slug
  chapter
+ framework
+ language
  }
  }
  site {
@@ -318,6 +338,7 @@ export const query = graphql`
  toc
  githubUrl
  codeGithubUrl
+ siteUrl
  }
  }
  pages: allMarkdownRemark(