diff --git a/spec/services/user_locale_setter_spec.rb b/spec/services/user_locale_setter_spec.rb
new file mode 100644
index 0000000000..443e6e2f7f
--- /dev/null
+++ b/spec/services/user_locale_setter_spec.rb
@@ -0,0 +1,157 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe UserLocaleSetter do
+  let(:user) { create(:user) }
+  let(:default_locale) { I18n.default_locale }
+  let(:locale_params) { {} }
+  let(:cookies) { {} }
+  let(:service) { UserLocaleSetter.new(user, locale_params, cookies) }
+
+  describe "#set_locale" do
+    describe "persists selected locale from params" do
+      let(:locale_params) { "es" }
+
+      context "when the user is logged in" do
+        it "saves selected locale to user.locale and cookies[:locale]" do
+          service.set_locale
+
+          expect(user.reload.locale).to eq "es"
+          expect(cookies).to eq({ locale: "es" })
+        end
+      end
+
+      context "when the user is not logged in" do
+        it "saves selected locale to cookies[:locale]" do
+          service.set_locale
+
+          expect(cookies).to eq({ locale: "es" })
+        end
+      end
+    end
+
+    describe "sets the current locale" do
+      context "when the user is logged in" do
+        context "and has a valid locale saved" do
+          before { user.update(locale: "es") }
+
+          it "applies the user's locale" do
+            service.set_locale
+
+            expect(I18n.locale).to eq :es
+          end
+        end
+
+        context "and has an invalid locale saved" do
+          before { user.update(locale: "xx") }
+
+          it "applies the default locale" do
+            service.set_locale
+
+            expect(I18n.locale).to eq I18n.default_locale
+          end
+        end
+
+        context "and has no locale saved" do
+          before { user.update(locale: nil) }
+
+          it "applies the locale from cookies if present" do
+            cookies[:locale] = "es"
+            service.set_locale
+
+            expect(I18n.locale).to eq :es
+          end
+
+          it "applies the default locale otherwise " do
+            service.set_locale
+
+            expect(I18n.locale).to eq I18n.default_locale
+          end
+        end
+      end
+
+      context "when the user is not logged in" do
+        let(:user) { nil }
+
+        context "with a locale set in cookies" do
+          it "applies the value from cookies" do
+            cookies[:locale] = "es"
+            service.set_locale
+
+            expect(I18n.locale).to eq :es
+          end
+        end
+
+        context "with no locale set in cookies" do
+          it "applies the default locale" do
+            service.set_locale
+
+            expect(I18n.locale).to eq I18n.default_locale
+          end
+        end
+      end
+    end
+  end
+
+  describe "#ensure_valid_locale_persisted" do
+    context "when a user is present" do
+      context "and has an unavailable locale saved" do
+        before { user.update(locale: "xx") }
+
+        context "with no locale set in cookies" do
+          it "set the user's locale to the default" do
+            service.ensure_valid_locale_persisted
+
+            expect(user.reload.locale).to eq default_locale.to_s
+          end
+        end
+
+        context "with a locale set in cookies" do
+          let(:cookies) { {locale: "es"} }
+
+          it "set the user's locale to the cookie value" do
+            service.ensure_valid_locale_persisted
+
+            expect(user.reload.locale).to eq "es"
+          end
+        end
+      end
+    end
+  end
+
+  describe "self#valid_locale_for_user" do
+    context "when the user has a locale set" do
+      it "returns the user's locale" do
+        user.update(locale: "es")
+        expect(UserLocaleSetter.valid_locale_for_user(user)).to eq "es"
+      end
+    end
+
+    context "when the user has no locale set" do
+      it "returns the default locale" do
+        expect(UserLocaleSetter.valid_locale_for_user(user)).to eq default_locale
+      end
+    end
+
+    context "when the given user argument is nil" do
+      it "returns the default locale" do
+        expect(UserLocaleSetter.valid_locale_for_user(nil)).to eq default_locale
+      end
+    end
+  end
+
+  describe "self#available_locale?" do
+    it "returns true if locale is available" do
+      expect(UserLocaleSetter.available_locale?("es")).to be true
+    end
+
+    it "returns false if locale is not available" do
+      expect(UserLocaleSetter.available_locale?("xx")).to be false
+    end
+
+    it "returns false if nil is given for locale" do
+      expect(UserLocaleSetter.available_locale?(nil)).to be false
+    end
+  end
+end