Check English translation if language doesn't exist (#361)

Need this because of https://github.com/facebook/Docusaurus/pull/316

lib/server/translate.js

@@ -26,22 +26,26 @@ function setLanguage(lang) {
   language = lang;
 }
 
+function doesTranslationExist(str, lang) {
+  return (
+    translation[lang] &&
+    translation[lang]['pages-strings'] &&
+    translation[lang]['pages-strings'][str]
+  );
+}
+
 function translate(str) {
   if (!language || language === '') {
+    // Check English, just in case; otherwise, just return the raw string back
+    if (doesTranslationExist(str, 'en')) {
+      return parseEscapeSequences(translation['en']['pages-strings'][str]);
+    }
     return str;
   }
 
-  if (
+  if (!doesTranslationExist(str, language)) {
-    !translation[language] ||
-    !translation[language]['pages-strings'] ||
-    !translation[language]['pages-strings'][str]
-  ) {
     // if a translated string doesn't exist, but english does then fallback
-    if (
+    if (doesTranslationExist(str, 'en')) {
-      translation['en'] &&
-      translation['en']['pages-strings'] &&
-      translation['en']['pages-strings'][str]
-    ) {
       console.error(
         "Could not find a string translation in '" +
           language +