From 0339f0a0c92cea6047a68055777a0e44421bcf41 Mon Sep 17 00:00:00 2001
From: Paulo Esteves <pjesteves@outlook.pt>
Date: Sun, 15 Aug 2021 00:27:10 +0100
Subject: [PATCH] Fix lang() function is overriding locale

---
 system/Common.php                      | 21 +++++++++++++++++++--
 tests/system/Language/LanguageTest.php | 19 +++++++++++++++++++
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/system/Common.php b/system/Common.php
index 77b8adcffbb0..9a5f50b2635b 100644
--- a/system/Common.php
+++ b/system/Common.php
@@ -763,8 +763,25 @@ function is_really_writable(string $file): bool
      */
     function lang(string $line, array $args = [], string $locale = null)
     {
-        return Services::language($locale)
-            ->getLine($line, $args);
+        $language = Services::language();
+
+        //Get active locale
+        $activeLocale = $language->getLocale();
+
+        if ($locale && $locale != $activeLocale)
+        {
+            $language->setLocale($locale);
+        }
+
+        $line = $language->getLine($line, $args);
+
+        if ($locale && $locale != $activeLocale)
+        {
+            //Reset to active locale
+            $language->setLocale($activeLocale);
+        }
+
+        return $line;
     }
 }
 
diff --git a/tests/system/Language/LanguageTest.php b/tests/system/Language/LanguageTest.php
index 06152922c3a2..a3a39073acb9 100644
--- a/tests/system/Language/LanguageTest.php
+++ b/tests/system/Language/LanguageTest.php
@@ -288,6 +288,25 @@ public function testBaseFallbacks()
 
     //--------------------------------------------------------------------
 
+    /**
+     * Test if after using lang() with a locale the Language class keep the locale after return the $line
+     */
+    public function testLangKeepLocale()
+    {
+        $this->lang = Services::language('en', true);
+
+        lang('Language.languageGetLineInvalidArgumentException');
+        $this->assertEquals('en', $this->lang->getLocale());
+
+        lang('Language.languageGetLineInvalidArgumentException', [], 'ru');
+        $this->assertEquals('en', $this->lang->getLocale());
+
+        lang('Language.languageGetLineInvalidArgumentException');
+        $this->assertEquals('en', $this->lang->getLocale());
+    }
+
+    //--------------------------------------------------------------------
+
     /**
      * Testing base locale vs variants, with fallback to English.
      *