feat(errors): dynamic fallback locale

app.js

@@ -11,7 +11,7 @@ const helmet = require('helmet')
 require('dotenv').config({ path: 'variables.env' })
 
 const helpers = require('./helpers')
-const { translate, initializeTranslations } = require('./i18n/i18n')
+const { translate, initializeTranslations, setFallbackLocale } = require('./i18n/i18n')
 const breadcrumb = require('./lib/breadcrumb')
 const { updateCookie } = require('./lib/cookies')
 const settings = require('./lib/settings')
@@ -110,6 +110,10 @@ app.use(catchErrors(async function (request, response, next) {
       response.locals.currentLocale = defaultLocale
     }
 
+    if (response.locals.fallbackCode) {
+      setFallbackLocale(response.locals.fallbackCode)
+    }
+
     // Creates a query string which adds the current credentials to links
     // To other implementations of this app in the about modal
     helpers.updateSettingsQuery(request, response, response.locals.settings)

i18n/i18n.js

@@ -2,12 +2,19 @@ const fs = require('fs')
 const path = require('path')
 
 let translations = null
-// Initializes translation dictionary with contents from /public/locales
-module.exports.initializeTranslations = () => {
+let fallbackLocale = null
+
+/**
+ * Initializes translation dictionary with contents from /public/locales
+ */
+function initializeTranslations () {
   if (translations) {
     return
   }
 
+  // Default fallbock locale is english
+  setFallbackLocale('en-US')
+
   translations = {}
 
   const localesPath = path.join(__dirname, 'locales')
@@ -26,6 +33,14 @@ module.exports.initializeTranslations = () => {
   }
 }
 
+/**
+ * Sets the fallback locale
+ * @param locale string Locale code
+ */
+function setFallbackLocale (locale) {
+  fallbackLocale = locale
+}
+
 /**
  * Translate a static string
  * @param symbol string Identifier for static text
@@ -33,14 +48,20 @@ module.exports.initializeTranslations = () => {
  *
  * @returns string
  */
-module.exports.translate = (symbol, locale = 'en-US') => {
+function translate (symbol, locale = 'en-US') {
   const localeDict = translations[locale]
-  if (!localeDict) {
-    return `Localization file for ${locale} is not available`
+  let translatedValue
+
+  if (localeDict) {
+    translatedValue = localeDict[symbol]
   }
-  const translatedValue = localeDict[symbol]
+
   if (!translatedValue) {
-    return `Translation not found for ${symbol} in ${locale}`
+    translatedValue = translations[fallbackLocale][symbol]
+  }
+
+  if (!translatedValue) {
+    return `Translation not found for ${symbol}`
   }
 
   return translatedValue
@@ -53,6 +74,11 @@ module.exports.translate = (symbol, locale = 'en-US') => {
  *
  * @returns boolean
  */
-module.exports.translationAvaliable = (symbol, locale = 'en-US') => {
-  return !!(translations[locale] || {})[symbol]
+function translationAvaliable (symbol, locale = 'en-US') {
+  return !!(translations[locale] || translations[fallbackLocale] || {})[symbol]
 }
+
+module.exports.initializeTranslations = initializeTranslations
+module.exports.setFallbackLocale = setFallbackLocale
+module.exports.translate = translate
+module.exports.translationAvaliable = translationAvaliable

test/unit/index.test.js

@@ -99,12 +99,12 @@ describe('Settings', () => {
 })
 
 describe('i18n', () => {
-  test('It returns an error when locale file is not found', () => {
-    expect(translate('foo', 'bar-locale')).toBe('Localization file for bar-locale is not available')
+  test('It returns the fallback value when locale file is not found', () => {
+    expect(translate('defaultTitle', 'not-existing-locale-file')).toBe('The Example App')
   })
 
   test('It returns an error when symbol is not found on locale file', () => {
-    expect(translate('foo', 'en-US')).toBe('Translation not found for foo in en-US')
+    expect(translate('foo', 'en-US')).toBe('Translation not found for foo')
   })
 
   test('It returns the translated string when symbol is found on locale file', () => {
@@ -113,10 +113,8 @@ describe('i18n', () => {
   test('It returns true if string is found for locale', () => {
     expect(translationAvaliable('coursesLabel', 'en-US')).toBe(true)
   })
-  test('It returns false if string is not found for locale', () => {
-    expect(translationAvaliable('foo-symbol', 'en-US')).toBe(false)
-  })
   test('It returns false if locale is not found', () => {
-    expect(translationAvaliable('coursesLabel', 'foo-locale')).toBe(false)
+    expect(translationAvaliable('foo-symbol', 'en-US')).toBe(false)
+    expect(translationAvaliable('foo-symbol', 'not-existing-locale')).toBe(false)
   })
 })