gatsby-node.js

const path = require('path');

// this is copied from gatsby-plugin-remove-trailing-slashes because it causes the build to fail if it is used direcly
const removeTrailingSlash = _path =>
  _path === '/' ? _path : _path.replace(/\/$/, '');

exports.onCreateWebpackConfig = ({ actions }) => {
  actions.setWebpackConfig({
    resolve: {
      modules: [path.resolve(__dirname, 'src'), 'node_modules'],
    },
  });
};

// workaround because gatsby seems to have issues with using ES module imports
// and mixing of CJS and ES does not work
const languages = {
  de: 'Deutsch',
  en: 'English',
};

exports.createPages = ({ actions, graphql }) => {
  const { createPage } = actions;

  const blogPostTemplate = path.resolve(`src/templates/blogTemplate.js`);

  return graphql(`
    {
      allMarkdownRemark(limit: 1000) {
        edges {
          node {
            frontmatter {
              path
              locale
              originalPath
            }
          }
        }
      }
    }
  `).then(result => {
    if (result.errors) {
      return Promise.reject(result.errors);
    }

    return result.data.allMarkdownRemark.edges.forEach(({ node }) => {
      const context = {
        languages,
        locale: node.frontmatter.locale,
        routed: true,
        originalPath: node.frontmatter.originalPath,
      };

      createPage({
        path: node.frontmatter.path,
        component: blogPostTemplate,
        context,
      });
    });
  });
};

exports.onCreatePage = ({ page, actions }) => {
  const { createPage, deletePage } = actions;

  // if (page.path.includes('404')) {
  //     return Promise.resolve();
  // }

  if (!page.componentPath.includes('src/pages')) {
    return Promise.resolve();
  }

  const oldPage = Object.assign({}, page);
  page.path = removeTrailingSlash(page.path);

  return new Promise(resolve => {
    const redirect = path.resolve('./src/i18n/Redirect.js');
    const redirectPage = {
      ...page,
      component: redirect,
      path: '/',
      context: {
        languages,
        locale: 'en',
        routed: false,
        redirectPage: page.path,
      },
    };
    createPage(redirectPage);

    if (page.path !== oldPage.path) {
      deletePage(oldPage);
    }

    Object.keys(languages).forEach(locale => {
      const context = {
        languages,
        locale,
        routed: true,
        originalPath: page.path,
      };

      const localePage = {
        ...page,
        originalPath: page.path,
        path: `/${locale}${page.path}`,
        context,
      };
      createPage(localePage);
    });

    resolve();
  });
};