From e264dca1e91ec83af5263cce7152d4101660daf4 Mon Sep 17 00:00:00 2001
From: jonian <jonian@hardpixel.eu>
Date: Mon, 4 Jan 2021 15:32:12 +0200
Subject: [PATCH 1/4] update multi-threaded fallbacks test

---
 test/backend/fallbacks_test.rb | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/test/backend/fallbacks_test.rb b/test/backend/fallbacks_test.rb
index 99565580..a3b0dcd0 100644
--- a/test/backend/fallbacks_test.rb
+++ b/test/backend/fallbacks_test.rb
@@ -109,8 +109,18 @@ def setup
   end
 
   test "multi-threaded fallbacks" do
-    Thread.new do
+    I18n.fallbacks = [:en]
 
+    thread = Thread.new do
+      I18n.fallbacks = [:de]
+    end
+
+    begin
+      thread.join
+      assert_equal 'Bar in :en', I18n.t(:bar, :locale => :'pt-BR')
+    ensure
+      thread.exit
+      I18n.fallbacks = I18n::Locale::Fallbacks.new
     end
   end
 end

From 1f2e32829321fd9faf9be285ba51d43d9a06c5d6 Mon Sep 17 00:00:00 2001
From: jonian <jonian@hardpixel.eu>
Date: Mon, 4 Jan 2021 16:10:36 +0200
Subject: [PATCH 2/4] store fallbacks in Thread.current and fetch with
 @@fallbacks as default

---
 lib/i18n/backend/fallbacks.rb | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/i18n/backend/fallbacks.rb b/lib/i18n/backend/fallbacks.rb
index ce8635bb..b6437620 100644
--- a/lib/i18n/backend/fallbacks.rb
+++ b/lib/i18n/backend/fallbacks.rb
@@ -16,11 +16,13 @@ class << self
     # Returns the current fallbacks implementation. Defaults to +I18n::Locale::Fallbacks+.
     def fallbacks
       @@fallbacks ||= I18n::Locale::Fallbacks.new
+      Thread.current.fetch(:i18n_fallbacks, @@fallbacks)
     end
 
     # Sets the current fallbacks implementation. Use this to set a different fallbacks implementation.
     def fallbacks=(fallbacks)
       @@fallbacks = fallbacks.is_a?(Array) ? I18n::Locale::Fallbacks.new(fallbacks) : fallbacks
+      Thread.current[:i18n_fallbacks] = @@fallbacks
     end
   end
 

From 9d4ee1abf34b5a7de4092d1643ddcf2f5ef7f759 Mon Sep 17 00:00:00 2001
From: jonian <jonian@hardpixel.eu>
Date: Mon, 4 Jan 2021 16:37:51 +0200
Subject: [PATCH 3/4] make thread key fetching compatible with older rubies

---
 lib/i18n/backend/fallbacks.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/i18n/backend/fallbacks.rb b/lib/i18n/backend/fallbacks.rb
index b6437620..ed2f7196 100644
--- a/lib/i18n/backend/fallbacks.rb
+++ b/lib/i18n/backend/fallbacks.rb
@@ -16,7 +16,7 @@ class << self
     # Returns the current fallbacks implementation. Defaults to +I18n::Locale::Fallbacks+.
     def fallbacks
       @@fallbacks ||= I18n::Locale::Fallbacks.new
-      Thread.current.fetch(:i18n_fallbacks, @@fallbacks)
+      Thread.current.key?(:i18n_fallbacks) ? Thread.current[:i18n_fallbacks] : @@fallbacks
     end
 
     # Sets the current fallbacks implementation. Use this to set a different fallbacks implementation.

From 45bbb7dd1c88285858794a862d7dc053a0d5abb3 Mon Sep 17 00:00:00 2001
From: jonian <jonian@hardpixel.eu>
Date: Mon, 4 Jan 2021 16:52:39 +0200
Subject: [PATCH 4/4] fix thread key fetching

---
 lib/i18n/backend/fallbacks.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/i18n/backend/fallbacks.rb b/lib/i18n/backend/fallbacks.rb
index ed2f7196..7688c13d 100644
--- a/lib/i18n/backend/fallbacks.rb
+++ b/lib/i18n/backend/fallbacks.rb
@@ -16,7 +16,7 @@ class << self
     # Returns the current fallbacks implementation. Defaults to +I18n::Locale::Fallbacks+.
     def fallbacks
       @@fallbacks ||= I18n::Locale::Fallbacks.new
-      Thread.current.key?(:i18n_fallbacks) ? Thread.current[:i18n_fallbacks] : @@fallbacks
+      Thread.current[:i18n_fallbacks] || @@fallbacks
     end
 
     # Sets the current fallbacks implementation. Use this to set a different fallbacks implementation.