From e5dab19844cef1051a0eac187a9f6765f063ccd0 Mon Sep 17 00:00:00 2001
From: Veloman Yunkan <veloman.yunkan@gmail.com>
Date: Sun, 28 Jan 2024 17:51:50 +0400
Subject: [PATCH] Default UI language is resolved in the frontend

This change eliminates any need for defaultUserLanguage in
viewer_settings.js.
---
 static/skin/i18n.js | 24 ++++++++++++++++++++++--
 test/server.cpp     |  6 +++---
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/static/skin/i18n.js b/static/skin/i18n.js
index e937eda3e..ed92d6f34 100644
--- a/static/skin/i18n.js
+++ b/static/skin/i18n.js
@@ -104,11 +104,31 @@ const DEFAULT_UI_LANGUAGE = 'en';
 
 Translations.load(DEFAULT_UI_LANGUAGE, /*asDefault=*/true);
 
+// Below function selects the most suitable UI language from the list
+// of preferred languages in browser preferences and available translations.
+// Since, unlike Accept-Language header, navigator.languages doesn't contain
+// qvalues, they are computed using the same algorithm as in Firefox 121
+function getDefaultUserLanguage() {
+  const mostSuitableLang = { code: DEFAULT_UI_LANGUAGE, score: 0 }
+  const n = navigator.languages.length;
+  for (const lang of uiLanguages ) {
+    const rank = navigator.languages.indexOf(lang.iso_code);
+    if ( rank >= 0 ) {
+      const qvalue = Math.round(10*(1 - rank/n))/10;
+      const score = qvalue * lang.translation_count;
+      if ( score > mostSuitableLang.score ) {
+        mostSuitableLang.code = lang.iso_code;
+        mostSuitableLang.score = score;
+      }
+    }
+  }
+  return mostSuitableLang.code;
+}
+
 function getUserLanguage() {
   return new URLSearchParams(window.location.search).get('userlang')
       || window.localStorage.getItem('userlang')
-      || viewerSettings.defaultUserLanguage
-      || DEFAULT_UI_LANGUAGE;
+      || getDefaultUserLanguage();
 }
 
 function setUserLanguage(lang, callback) {
diff --git a/test/server.cpp b/test/server.cpp
index c22bffe88..74e082c16 100644
--- a/test/server.cpp
+++ b/test/server.cpp
@@ -59,7 +59,7 @@ const ResourceCollection resources200Compressible{
   { DYNAMIC_CONTENT, "/ROOT%23%3F/skin/autoComplete/css/autoComplete.css" },
   { STATIC_CONTENT,  "/ROOT%23%3F/skin/autoComplete/css/autoComplete.css?cacheid=ef30cd42" },
   { DYNAMIC_CONTENT, "/ROOT%23%3F/skin/i18n.js" },
-  { STATIC_CONTENT,  "/ROOT%23%3F/skin/i18n.js?cacheid=0b99e7a9" },
+  { STATIC_CONTENT,  "/ROOT%23%3F/skin/i18n.js?cacheid=071abc9a" },
   { DYNAMIC_CONTENT, "/ROOT%23%3F/skin/index.css" },
   { STATIC_CONTENT,  "/ROOT%23%3F/skin/index.css?cacheid=1e78e7cf" },
   { DYNAMIC_CONTENT, "/ROOT%23%3F/skin/index.js" },
@@ -285,7 +285,7 @@ R"EXPECTEDRESULT(      href="/ROOT%23%3F/skin/kiwix.css?cacheid=2158fad9"
     <link rel="mask-icon" href="/ROOT%23%3F/skin/favicon/safari-pinned-tab.svg?cacheid=8d487e95" color="#5bbad5">
     <link rel="shortcut icon" href="/ROOT%23%3F/skin/favicon/favicon.ico?cacheid=92663314">
     <meta name="msapplication-config" content="/ROOT%23%3F/skin/favicon/browserconfig.xml?cacheid=f29a7c4a">
-    <script type="module" src="/ROOT%23%3F/skin/i18n.js?cacheid=0b99e7a9" defer></script>
+    <script type="module" src="/ROOT%23%3F/skin/i18n.js?cacheid=071abc9a" defer></script>
     <script type="text/javascript" src="/ROOT%23%3F/skin/languages.js?cacheid=c41aae47" defer></script>
     <script src="/ROOT%23%3F/skin/isotope.pkgd.min.js?cacheid=2e48d392" defer></script>
     <script src="/ROOT%23%3F/skin/iso6391To3.js?cacheid=ecde2bb3"></script>
@@ -318,7 +318,7 @@ R"EXPECTEDRESULT(                                <img src="${root}/skin/download
 R"EXPECTEDRESULT(    <link type="text/css" href="./skin/kiwix.css?cacheid=2158fad9" rel="Stylesheet" />
     <link type="text/css" href="./skin/taskbar.css?cacheid=e014a885" rel="Stylesheet" />
     <link type="text/css" href="./skin/autoComplete/css/autoComplete.css?cacheid=ef30cd42" rel="Stylesheet" />
-    <script type="module" src="./skin/i18n.js?cacheid=0b99e7a9" defer></script>
+    <script type="module" src="./skin/i18n.js?cacheid=071abc9a" defer></script>
     <script type="text/javascript" src="./skin/languages.js?cacheid=c41aae47" defer></script>
     <script type="text/javascript" src="./skin/viewer.js?cacheid=e9c025f2" defer></script>
     <script type="text/javascript" src="./skin/autoComplete/autoComplete.min.js?cacheid=1191aaaf"></script>