JIT choose default docs language and persist user selections with localStorage

plugins/gatsby-plugin-crowdin/onCreatePage.js

@@ -97,7 +97,7 @@ module.exports = ({page, boundActionCreators}, pluginOptions) => {
 
     createRedirect({
       fromPath: nonLocalizedPath,
-      toPath: path,
+      toPath: `/docs-language-redirect/?${nonLocalizedPath}`,
       redirectInBrowser: true,
       Language: language,
     });

src/pages/docs-language-redirect.js

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ *
+ * @emails react-core
+ */
+
+import React from 'react';
+import PropTypes from 'prop-types';
+import {Redirect} from 'react-router-dom';
+import {getSelectedLanguage} from 'utils/languageUtils';
+
+const DocsRedirect = ({location}) => {
+  // Redirect the user to their most recent locale, or English as a fallback.
+  const language = getSelectedLanguage();
+
+  return <Redirect to={`/${language}${location.search.substr(1)}`} />;
+};
+
+DocsRedirect.propTypes = {
+  location: PropTypes.object.isRequired,
+};
+
+export default DocsRedirect;

src/pages/translations.js

@@ -11,9 +11,7 @@ import TitleAndMetaTags from 'components/TitleAndMetaTags';
 import Link from 'gatsby-link';
 import React from 'react';
 import {sharedStyles} from 'theme';
-
-// $FlowFixMe This is a valid path
-import languages from '../../crowdin/languages.json';
+import {getTranslatedLanguages} from 'utils/languageUtils';
 
 const Translations = () => (
   <Container>
@@ -27,7 +25,7 @@ const Translations = () => (
             languages:
           </p>
           <ul>
-            {languages.map(language => (
+            {getTranslatedLanguages().map(language => (
               <li key={language}>
                 <Link to={`/${language}/docs/hello-world.html`}>
                   {language}

src/templates/docs.js

@@ -9,16 +9,26 @@ import PropTypes from 'prop-types';
 import React from 'react';
 import {createLinkDocs} from 'utils/createLink';
 import {sectionListDocs} from 'utils/sectionList';
+import {setSelectedLanguage} from 'utils/languageUtils';
 
-const Docs = ({data, location}) => (
-  <MarkdownPage
-    createLink={createLinkDocs}
-    location={location}
-    markdownRemark={data.markdownRemark}
-    sectionList={sectionListDocs}
-    titlePostfix=" - React"
-  />
-);
+const Docs = ({data, location}) => {
+  // Store the user's most recent locale based on the current URL.
+  // We'll restore this language when they visit a new (unlocalized) URL.
+  const matches = location.pathname.substr(1).split('/');
+  if (matches.length > 1) {
+    setSelectedLanguage(matches[0]);
+  }
+
+  return (
+    <MarkdownPage
+      createLink={createLinkDocs}
+      location={location}
+      markdownRemark={data.markdownRemark}
+      sectionList={sectionListDocs}
+      titlePostfix=" - React"
+    />
+  );
+};
 
 Docs.propTypes = {
   data: PropTypes.object.isRequired,

src/utils/createLink.js

@@ -24,7 +24,6 @@ type CreateLinkBaseProps = {
 
 const createLinkBlog = ({
   isActive,
-  isLocalized,
   item,
   location,
   section,
@@ -32,7 +31,6 @@ const createLinkBlog = ({
   return (
     <Link
       css={[linkCss, isActive && activeLinkCss]}
-      isLocalized={isLocalized}
       location={location}
       to={item.id}>
       {isActive && <span css={activeLinkBefore} />}
@@ -43,7 +41,6 @@ const createLinkBlog = ({
 
 const createLinkCommunity = ({
   isActive,
-  isLocalized,
   item,
   location,
   section,
@@ -65,7 +62,7 @@ const createLinkCommunity = ({
   }
   return createLinkDocs({
     isActive,
-    isLocalized,
+    isLocalized: false,
     item,
     location,
     section,
@@ -97,7 +94,6 @@ type CreateLinkTutorialProps = {
 
 const createLinkTutorial = ({
   isActive,
-  isLocalized,
   item,
   location,
   onLinkClick,
@@ -106,7 +102,6 @@ const createLinkTutorial = ({
   return (
     <Link
       css={[linkCss, isActive && activeLinkCss]}
-      isLocalized={isLocalized}
       location={location}
       onClick={onLinkClick}
       to={item.href}>

src/utils/languageUtils.js

@@ -0,0 +1,46 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ *
+ * @emails react-core
+ * @flow
+ */
+
+// $FlowFixMe This is a valid path
+import languagesArray from '../../crowdin/languages.json';
+
+const DEFAULT_LANGUAGE = 'en-US';
+
+const languagesMap = languagesArray.reduce((map: Object, language: string) => {
+  map[language] = true;
+  return map;
+}, Object.create(null));
+
+export function getTranslatedLanguages(): Array<string> {
+  return languagesArray;
+}
+
+export function getSelectedLanguage(): string {
+  let language = localStorage.getItem('selectedLanguage');
+  if (languagesMap[language]) {
+    return ((language: any): string);
+  } else {
+    const {languages} = navigator;
+    for (let i = 0; i < languages.length; i++) {
+      language = languages[i];
+      if (languagesMap[language]) {
+        return language;
+      }
+    }
+  }
+  return DEFAULT_LANGUAGE;
+}
+
+export function setSelectedLanguage(language: string): void {
+  if (languagesMap[language]) {
+    localStorage.setItem('selectedLanguage', language);
+  } else if (process.env.NODE_ENV !== 'production') {
+    console.warn(
+      `Specified language "${language}" is not a valid translation.`,
+    );
+  }
+}