diff --git a/app/controllers/first_steps_controller.rb b/app/controllers/first_steps_controller.rb
index 53a350ef1..4af07aed1 100644
--- a/app/controllers/first_steps_controller.rb
+++ b/app/controllers/first_steps_controller.rb
@@ -177,7 +177,7 @@ class FirstStepsController < ApplicationController
     original_user_id = UserInfo.current_user_id
     result = NotificationFactory::Mailer.template(
       template: 'test_ticket',
-      locale:   agent.preferences[:locale] || Setting.get('locale_default') || 'en-us',
+      locale:   agent.locale,
       objects:  {
         agent:    agent,
         customer: customer,
diff --git a/app/models/locale.rb b/app/models/locale.rb
index 26dbcd1e7..a00258174 100644
--- a/app/models/locale.rb
+++ b/app/models/locale.rb
@@ -119,6 +119,14 @@ all:
     result.data
   end
 
+  #  Default system locale
+  #
+  #  @example
+  #    Locale.default
+  def self.default
+    Setting.get('locale_default') || 'en-us'
+  end
+
   private_class_method def self.to_database(data)
     ActiveRecord::Base.transaction do
       data.each do |locale|
diff --git a/app/models/ticket.rb b/app/models/ticket.rb
index 873bf2757..cfd11bfde 100644
--- a/app/models/ticket.rb
+++ b/app/models/ticket.rb
@@ -1462,7 +1462,6 @@ result
     # get subject
     subject = NotificationFactory::Mailer.template(
       templateInline: value['subject'],
-      locale:         'en-en',
       objects:        objects,
       quote:          false,
     )
@@ -1470,7 +1469,6 @@ result
 
     body = NotificationFactory::Mailer.template(
       templateInline: value['body'],
-      locale:         'en-en',
       objects:        objects,
       quote:          true,
     )
@@ -1561,8 +1559,6 @@ result
     objects = build_notification_template_objects(article)
     body = NotificationFactory::Renderer.new(
       objects:  objects,
-      locale:   'en-en',
-      timezone: Setting.get('timezone_default'),
       template: value['body'],
       escape:   false
     ).render.html2text.tr(' ', ' ') # convert non-breaking space to simple space
diff --git a/app/models/transaction/notification.rb b/app/models/transaction/notification.rb
index d045ee5f6..dcf9bd57b 100644
--- a/app/models/transaction/notification.rb
+++ b/app/models/transaction/notification.rb
@@ -235,7 +235,7 @@ class Transaction::Notification
 
     return {} if !@item[:changes]
 
-    locale = user.preferences[:locale] || Setting.get('locale_default') || 'en-us'
+    locale = user.locale
 
     # only show allowed attributes
     attribute_list = ObjectManager::Attribute.by_object_as_hash('Ticket', user)
diff --git a/app/models/transaction/slack.rb b/app/models/transaction/slack.rb
index 19c984922..ab915301c 100644
--- a/app/models/transaction/slack.rb
+++ b/app/models/transaction/slack.rb
@@ -86,8 +86,8 @@ class Transaction::Slack
 
     result = NotificationFactory::Slack.template(
       template: template,
-      locale:   user[:preferences][:locale] || Setting.get('locale_default'),
-      timezone: user[:preferences][:timezone] || Setting.get('timezone_default'),
+      locale:   user.locale,
+      timezone: Setting.get('timezone_default'),
       objects:  {
         ticket:       ticket,
         article:      article,
diff --git a/app/models/translation.rb b/app/models/translation.rb
index aa0ae6d96..4dd8d2432 100644
--- a/app/models/translation.rb
+++ b/app/models/translation.rb
@@ -237,14 +237,15 @@ or
       end
     end
 
-    record = Translation.where(locale: locale, source: 'timestamp', format: 'time').pluck(:target).first
-    return timestamp.to_s if !record
-
     begin
       timestamp = timestamp.in_time_zone(timezone)
     rescue
       return timestamp.to_s
     end
+
+    record = Translation.where(locale: locale, source: 'timestamp', format: 'time').pluck(:target).first
+    return timestamp.to_s if !record
+
     record.sub!('dd', format('%02d', timestamp.day))
     record.sub!('d', timestamp.day.to_s)
     record.sub!('mm', format('%02d', timestamp.month))
diff --git a/app/models/user.rb b/app/models/user.rb
index 1ee4631a8..151a01a98 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -916,9 +916,9 @@ try to find correct name
     firstname.blank? && lastname.blank?
   end
 
-  # get locale of user or system if user's own is not set
+  # get locale identifier of user or system if user's own is not set
   def locale
-    preferences.fetch(:locale) { Setting.get('locale_default') }
+    preferences.fetch(:locale) { Locale.default }
   end
 
   private
diff --git a/lib/calendar_subscriptions/tickets.rb b/lib/calendar_subscriptions/tickets.rb
index 7c10af8e2..91058f990 100644
--- a/lib/calendar_subscriptions/tickets.rb
+++ b/lib/calendar_subscriptions/tickets.rb
@@ -76,7 +76,7 @@ class CalendarSubscriptions::Tickets
       condition:    condition,
     )
 
-    user_locale       = @user.preferences['locale'] || Setting.get('locale_default') || 'en-us'
+    user_locale       = @user.locale
     translated_ticket = Translation.translate(user_locale, 'ticket')
 
     events_data = []
@@ -126,7 +126,7 @@ class CalendarSubscriptions::Tickets
       condition:    condition,
     )
 
-    user_locale       = @user.preferences['locale'] || Setting.get('locale_default') || 'en-us'
+    user_locale       = @user.locale
     translated_ticket = Translation.translate(user_locale, 'ticket')
     customer          = Translation.translate(user_locale, 'customer')
 
@@ -183,7 +183,7 @@ class CalendarSubscriptions::Tickets
       condition:    condition,
     )
 
-    user_locale                  = @user.preferences['locale'] || Setting.get('locale_default') || 'en-us'
+    user_locale                  = @user.locale
     translated_ticket_escalation = Translation.translate(user_locale, 'ticket escalation')
     customer                     = Translation.translate(user_locale, 'customer')
 
diff --git a/lib/excel_sheet.rb b/lib/excel_sheet.rb
index 99e3ff710..ecf87b012 100644
--- a/lib/excel_sheet.rb
+++ b/lib/excel_sheet.rb
@@ -5,7 +5,7 @@ class ExcelSheet
     @header          = header
     @records         = records
     @timezone        = timezone.presence || Setting.get('timezone_default')
-    @locale          = locale || 'en-en'
+    @locale          = locale || Locale.default
     @tempfile        = Tempfile.new('excel-export.xls')
     @workbook        = WriteExcel.new(@tempfile)
     @worksheet       = @workbook.add_worksheet
diff --git a/lib/notification_factory.rb b/lib/notification_factory.rb
index 931799516..5831d0f5e 100644
--- a/lib/notification_factory.rb
+++ b/lib/notification_factory.rb
@@ -53,7 +53,7 @@ returns
   private_class_method :template_path
 
   def self.template_filenames(data)
-    locale = data[:locale] || Setting.get('locale_default') || 'en-us'
+    locale = data[:locale] || Locale.default
 
     [locale, locale[0, 2], 'en']
       .uniq
diff --git a/lib/notification_factory/mailer.rb b/lib/notification_factory/mailer.rb
index bf201f924..b6760839f 100644
--- a/lib/notification_factory/mailer.rb
+++ b/lib/notification_factory/mailer.rb
@@ -295,7 +295,7 @@ returns
     end
 
     template = NotificationFactory.template_read(
-      locale:   data[:locale] || Setting.get('locale_default') || 'en-us',
+      locale:   data[:locale] || Locale.default,
       template: data[:template],
       format:   data[:format] || 'html',
       type:     'mailer',
diff --git a/lib/notification_factory/renderer.rb b/lib/notification_factory/renderer.rb
index 2127c2473..37ba85a83 100644
--- a/lib/notification_factory/renderer.rb
+++ b/lib/notification_factory/renderer.rb
@@ -26,8 +26,8 @@ examples how to use
 =end
 
   def initialize(objects:, locale: nil, timezone: nil, template:, escape: true)
-    @objects = objects
-    @locale = locale || Setting.get('locale_default') || 'en-us'
+    @objects  = objects
+    @locale   = locale || Locale.default
     @timezone = timezone || Setting.get('timezone_default')
     @template = NotificationFactory::Template.new(template, escape)
     @escape = escape
diff --git a/lib/notification_factory/slack.rb b/lib/notification_factory/slack.rb
index 85542268e..51e918a4e 100644
--- a/lib/notification_factory/slack.rb
+++ b/lib/notification_factory/slack.rb
@@ -33,7 +33,7 @@ returns
     end
 
     template = NotificationFactory.template_read(
-      locale:   data[:locale] || Setting.get('locale_default') || 'en-us',
+      locale:   data[:locale] || Locale.default,
       template: data[:template],
       format:   'md',
       type:     'slack',
diff --git a/spec/models/locale_spec.rb b/spec/models/locale_spec.rb
new file mode 100644
index 000000000..f11225b81
--- /dev/null
+++ b/spec/models/locale_spec.rb
@@ -0,0 +1,23 @@
+require 'rails_helper'
+
+RSpec.describe Locale, type: :model do
+  describe 'Class methods:' do
+    describe '.default' do
+      context 'with default locale' do
+        before { Setting.set('locale_default', 'foo') }
+
+        it 'returns the system-wide default locale' do
+          expect(described_class.default).to eq('foo')
+        end
+      end
+
+      context 'without default locale' do
+        before { Setting.set('locale_default', nil) }
+
+        it 'returns en-us' do
+          expect(described_class.default).to eq('en-us')
+        end
+      end
+    end
+  end
+end
diff --git a/spec/models/translation_spec.rb b/spec/models/translation_spec.rb
index f823b735a..360a0864b 100644
--- a/spec/models/translation_spec.rb
+++ b/spec/models/translation_spec.rb
@@ -38,11 +38,11 @@ RSpec.describe Translation do
     end
 
     it 'not_existing with timestamp as string' do
-      expect(described_class.timestamp('not_existing', 'Europe/Berlin', '2018-10-10T10:00:00Z0')).to eq('2018-10-10 10:00:00 UTC')
+      expect(described_class.timestamp('not_existing', 'Europe/Berlin', '2018-10-10T10:00:00Z0')).to eq('2018-10-10 12:00:00 +0200')
     end
 
     it 'not_existing with time object' do
-      expect(described_class.timestamp('not_existing', 'Europe/Berlin', Time.zone.parse('2018-10-10T10:00:00Z0'))).to eq('2018-10-10 10:00:00 UTC')
+      expect(described_class.timestamp('not_existing', 'Europe/Berlin', Time.zone.parse('2018-10-10T10:00:00Z0'))).to eq('2018-10-10 12:00:00 +0200')
     end
 
     it 'not_existing with invalid timestamp string' do
diff --git a/spec/models/trigger/sms_spec.rb b/spec/models/trigger/sms_spec.rb
index 8c1854056..86bdffc51 100644
--- a/spec/models/trigger/sms_spec.rb
+++ b/spec/models/trigger/sms_spec.rb
@@ -3,29 +3,63 @@ require 'rails_helper'
 RSpec.describe Trigger do
 
   describe 'sms' do
+    before do
+      Translation.fetch(locale)
+      Setting.set('locale_default', locale)
+      Setting.set('timezone_default', time_zone)
+    end
 
-    it 'sends interpolated, html-free SMS' do
-      agent = create(:agent_user)
-      another_agent = create(:admin_user, mobile: '+37061010000')
-      Group.lookup(id: 1).users << another_agent
+    let(:time_zone) { 'Europe/Vilnius' }
+    let(:locale) { 'de-de' }
 
-      create(:channel, area: 'Sms::Notification')
-      create(:trigger,
-             disable_notification: false,
-             perform:              {
-               'notification.sms': {
-                 recipient: 'ticket_agents',
-                 body:      'space&nbsp;between #{ticket.title}', # rubocop:disable Lint/InterpolationCheck
-               }
-             })
+    context 'sends interpolated, html-free SMS' do
+      before do
+        another_agent = create(:admin_user, mobile: '+37061010000')
+        Group.lookup(id: 1).users << another_agent
 
-      ticket = create(:ticket, group: Group.lookup(id: 1), created_by_id: agent.id)
-      Observer::Transaction.commit
+        create(:channel, area: 'Sms::Notification')
+        create(:trigger,
+               disable_notification: false,
+               perform:              {
+                 'notification.sms': {
+                   recipient: 'ticket_agents',
+                   body:      message_body,
+                 }
+               })
+      end
 
-      triggered_article = Ticket::Article.last
+      let(:message_body) { 'space&nbsp;between #{ticket.title} #{ticket.created_at}' } # rubocop:disable Lint/InterpolationCheck
 
-      expect(triggered_article.body).to match(/space between/)
-      expect(triggered_article.body).to match(ticket.title)
+      let(:agent) { create(:agent_user) }
+      let(:ticket) do
+        ticket = create(:ticket, group: Group.lookup(id: 1), created_by_id: agent.id)
+        Observer::Transaction.commit
+        ticket
+      end
+
+      let(:triggered_article) do
+        ticket.articles.last
+      end
+
+      it 'renders HTML chars' do
+        expect(triggered_article.body).to match(/space between/)
+      end
+
+      it 'interpolates ticket properties' do
+        expect(triggered_article.body).to match(ticket.title)
+      end
+
+      it 'interpolates time in selected time zone' do
+        time_in_zone = triggered_article.ticket.created_at.in_time_zone(time_zone)
+
+        expect(triggered_article.body).to match(time_in_zone.strftime('%H:%M'))
+      end
+
+      it 'interpolates date in selected locale format' do
+        time_in_zone = triggered_article.ticket.created_at.in_time_zone(time_zone)
+
+        expect(triggered_article.body).to match(time_in_zone.strftime('%d.%m.%y'))
+      end
     end
   end
 end
diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
index c48892b2e..8c515559f 100644
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -647,10 +647,20 @@ RSpec.describe User, type: :model do
       context 'with no #preferences[:locale]' do
         let(:preferences) { {} }
 
-        before { Setting.set('locale_default', 'foo') }
+        context 'with default locale' do
+          before { Setting.set('locale_default', 'foo') }
 
-        it 'returns the system-wide default locale' do
-          expect(user.locale).to eq('foo')
+          it 'returns the system-wide default locale' do
+            expect(user.locale).to eq('foo')
+          end
+        end
+
+        context 'without default locale' do
+          before { Setting.set('locale_default', nil) }
+
+          it 'returns en-us' do
+            expect(user.locale).to eq('en-us')
+          end
         end
       end