diff --git a/js/src/chartviewmodel.js b/js/src/chartviewmodel.js
index b9f67ea..f84c549 100644
--- a/js/src/chartviewmodel.js
+++ b/js/src/chartviewmodel.js
@@ -17,10 +17,10 @@
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
+import { lang as $ } from './initializer.js';
 import Chartist from 'chartist'
 import ViewModel from './viewmodel.js';
 import ctAxisTitle from 'chartist-plugin-axistitle';
-import { lang } from './initializer.js';
 import uUtils from './utils.js';
 
 /**
@@ -81,7 +81,7 @@ export default class ChartViewModel extends ViewModel {
       plugins: [
         ctAxisTitle({
           axisY: {
-            axisTitle: `${lang.strings['altitude']} (${lang.unit('unitDistance')})`,
+            axisTitle: `${$._('altitude')} (${$.unit('unitDistance')})`,
             axisClass: 'ct-axis-title',
             offset: {
               x: 0,
diff --git a/js/src/configviewmodel.js b/js/src/configviewmodel.js
index 58cc6cd..ee3a3ad 100644
--- a/js/src/configviewmodel.js
+++ b/js/src/configviewmodel.js
@@ -17,7 +17,7 @@
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
-import { config, lang } from './initializer.js';
+import { lang as $, config } from './initializer.js';
 import ViewModel from './viewmodel.js';
 import uUtils from './utils.js';
 
@@ -61,7 +61,7 @@ export default class ConfigViewModel extends ViewModel {
   }
 
   setAutoReloadInterval() {
-    const interval = parseInt(prompt(lang.strings['newinterval']));
+    const interval = parseInt(prompt($._('newinterval')));
     if (!isNaN(interval) && interval !== this.model.interval) {
       this.model.interval = interval;
     }
diff --git a/js/src/lang.js b/js/src/lang.js
new file mode 100644
index 0000000..f5e899d
--- /dev/null
+++ b/js/src/lang.js
@@ -0,0 +1,128 @@
+/*
+ * μlogger
+ *
+ * Copyright(C) 2019 Bartek Fabiszewski (www.fabiszewski.net)
+ *
+ * This is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+export default class uLang {
+  constructor() {
+    this.strings = {};
+    this.config = null;
+  }
+
+  /**
+   * @param {uConfig} config
+   * @param {Object<string, string>} data
+   */
+  init(config, data) {
+    this.config = config;
+    if (data) {
+      /** @type {Object<string, string>} */
+      this.strings = data;
+    }
+  }
+
+  _(name) {
+    if (typeof this.strings[name] === 'undefined') {
+      throw new Error('Unknown localized string');
+    }
+    return this.strings[name];
+  }
+
+  /**
+   * @param {string} name
+   * @return {string}
+   */
+  unit(name) {
+    const unitName = this.config[name];
+    if (typeof this.config[name] === 'undefined') {
+      throw new Error('Unknown localized unit');
+    }
+    return this._(unitName);
+  }
+
+  /**
+   * Get speed converted to locale units
+   * @param {number} ms Speed in meters per second
+   * @param {boolean} withUnit
+   * @return {(number|string)} String when with unit
+   */
+  getLocaleSpeed(ms, withUnit) {
+    const value = Math.round(ms * this.config.factorSpeed * 360) / 100;
+    if (withUnit) {
+      return `${value} ${this.unit('unitSpeed')}`;
+    }
+    return value;
+  }
+
+  /**
+   * Get distance converted to locale units
+   * @param {number} m Distance in meters
+   * @param {boolean} withUnit
+   * @return {(number|string)} String when with unit
+   */
+  getLocaleDistanceMajor(m, withUnit) {
+    const value = Math.round(m * this.config.factorDistanceMajor / 10) / 100;
+    if (withUnit) {
+      return `${value} ${this.unit('unitDistanceMajor')}`
+    }
+    return value;
+  }
+
+  /**
+   * @param {number} m Distance in meters
+   * @param {boolean} withUnit
+   * @return {(number|string)} String when with unit
+   */
+  getLocaleDistance(m, withUnit) {
+    const value = Math.round(m * this.config.factorDistance * 100) / 100;
+    if (withUnit) {
+      return `${value} ${this.unit('unitDistance')}`;
+    }
+    return value;
+  }
+
+  /**
+   * @param {number} m Distance in meters
+   * @param {boolean} withUnit
+   * @return {(number|string)} String when with unit
+   */
+  getLocaleAltitude(m, withUnit) {
+    return this.getLocaleDistance(m, withUnit);
+  }
+
+  /**
+   * @param {number} m Distance in meters
+   * @param {boolean} withUnit
+   * @return {(number|string)} String when with unit
+   */
+  getLocaleAccuracy(m, withUnit) {
+    return this.getLocaleDistance(m, withUnit);
+  }
+
+  /**
+   * @param {number} s Duration in seconds
+   * @return {string} Formatted to (d) h:m:s
+   */
+  getLocaleDuration(s) {
+    const d = Math.floor(s / 86400);
+    const h = Math.floor((s % 86400) / 3600);
+    const m = Math.floor(((s % 86400) % 3600) / 60);
+    s = ((s % 86400) % 3600) % 60;
+    return ((d > 0) ? (`${d} ${this.unit('unitDay')} `) : '') +
+      ((`00${h}`).slice(-2)) + ':' + ((`00${m}`).slice(-2)) + ':' + ((`00${s}`).slice(-2)) + '';
+  }
+}
diff --git a/js/src/mapapi/api_gmaps.js b/js/src/mapapi/api_gmaps.js
index 04c575d..0190dcf 100644
--- a/js/src/mapapi/api_gmaps.js
+++ b/js/src/mapapi/api_gmaps.js
@@ -17,7 +17,7 @@
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
-import { config, lang } from '../initializer.js';
+import { lang as $, config } from '../initializer.js';
 import MapViewModel from '../mapviewmodel.js';
 import uTrack from '../track.js';
 import uUtils from '../utils.js';
@@ -74,9 +74,9 @@ export default class GoogleMapsApi {
       };
       window.gm_authFailure = () => {
         GoogleMapsApi.authError = true;
-        let message = uUtils.sprintf(lang.strings['apifailure'], 'Google Maps');
-        message += '<br><br>' + lang.strings['gmauthfailure'];
-        message += '<br><br>' + lang.strings['gmapilink'];
+        let message = uUtils.sprintf($._('apifailure'), 'Google Maps');
+        message += '<br><br>' + $._('gmauthfailure');
+        message += '<br><br>' + $._('gmapilink');
         if (GoogleMapsApi.gmInitialized) {
           alert(message);
         }
diff --git a/js/src/mapviewmodel.js b/js/src/mapviewmodel.js
index 4cde5bb..0d950e2 100644
--- a/js/src/mapviewmodel.js
+++ b/js/src/mapviewmodel.js
@@ -17,7 +17,7 @@
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
-import { config, lang } from './initializer.js';
+import { lang as $, config } from './initializer.js';
 import GoogleMapsApi from './mapapi/api_gmaps.js';
 import OpenLayersApi from './mapapi/api_openlayers.js';
 import ViewModel from './viewmodel.js';
@@ -78,7 +78,7 @@ export default class MapViewModel extends ViewModel {
     this.api.init()
       .then(() => this.onReady())
       .catch((e) => {
-        let txt = uUtils.sprintf(lang.strings['apifailure'], apiName);
+        let txt = uUtils.sprintf($._('apifailure'), apiName);
         if (e && e.message) {
           txt += ` (${e.message})`;
         }
@@ -134,36 +134,36 @@ export default class MapViewModel extends ViewModel {
     }
     let provider = '';
     if (pos.provider === 'gps') {
-      provider = ` (<img class="icon" alt="${lang.strings['gps']}" title="${lang.strings['gps']}"  src="images/gps_dark.svg">)`;
+      provider = ` (<img class="icon" alt="${$._('gps')}" title="${$._('gps')}"  src="images/gps_dark.svg">)`;
     } else if (pos.provider === 'network') {
-      provider = ` (<img class="icon" alt="${lang.strings['network']}" title="${lang.strings['network']}"  src="images/network_dark.svg">)`;
+      provider = ` (<img class="icon" alt="${$._('network')}" title="${$._('network')}"  src="images/network_dark.svg">)`;
     }
     let stats = '';
     if (!this.state.showLatest) {
       stats =
         `<div id="pright">
-        <img class="icon" alt="${lang.strings['track']}" src="images/stats_blue.svg" style="padding-left: 3em;"><br>
-        <img class="icon" alt="${lang.strings['ttime']}" title="${lang.strings['ttime']}" src="images/time_blue.svg"> ${lang.getLocaleDuration(pos.totalSeconds)}<br>
-        <img class="icon" alt="${lang.strings['aspeed']}" title="${lang.strings['aspeed']}" src="images/speed_blue.svg"> ${lang.getLocaleSpeed(pos.totalSpeed, true)}<br>
-        <img class="icon" alt="${lang.strings['tdistance']}" title="${lang.strings['tdistance']}" src="images/distance_blue.svg"> ${lang.getLocaleDistanceMajor(pos.totalMeters, true)}<br>
+        <img class="icon" alt="${$._('track')}" src="images/stats_blue.svg" style="padding-left: 3em;"><br>
+        <img class="icon" alt="${$._('ttime')}" title="${$._('ttime')}" src="images/time_blue.svg"> ${$.getLocaleDuration(pos.totalSeconds)}<br>
+        <img class="icon" alt="${$._('aspeed')}" title="${$._('aspeed')}" src="images/speed_blue.svg"> ${$.getLocaleSpeed(pos.totalSpeed, true)}<br>
+        <img class="icon" alt="${$._('tdistance')}" title="${$._('tdistance')}" src="images/distance_blue.svg"> ${$.getLocaleDistanceMajor(pos.totalMeters, true)}<br>
         </div>`;
     }
     return `<div id="popup">
         <div id="pheader">
-        <div><img alt="${lang.strings['user']}" title="${lang.strings['user']}" src="images/user_dark.svg"> ${uUtils.htmlEncode(pos.username)}</div>
-        <div><img alt="${lang.strings['track']}" title="${lang.strings['track']}" src="images/route_dark.svg"> ${uUtils.htmlEncode(pos.trackname)}</div>
+        <div><img alt="${$._('user')}" title="${$._('user')}" src="images/user_dark.svg"> ${uUtils.htmlEncode(pos.username)}</div>
+        <div><img alt="${$._('track')}" title="${$._('track')}" src="images/route_dark.svg"> ${uUtils.htmlEncode(pos.trackname)}</div>
         </div>
         <div id="pbody">
         ${(pos.hasComment()) ? `<div id="pcomments">${uUtils.htmlEncode(pos.comment)}</div>` : ''}
         ${(pos.hasImage()) ? `<div id="pimage"><img src="uploads/${pos.image}" alt="image"></div>` : ''}
         <div id="pleft">
-        <img class="icon" alt="${lang.strings['time']}" title="${lang.strings['time']}" src="images/calendar_dark.svg"> ${date}<br>
-        <img class="icon" alt="${lang.strings['time']}" title="${lang.strings['time']}" src="images/clock_dark.svg"> ${time}<br>
-        ${(pos.speed !== null) ? `<img class="icon" alt="${lang.strings['speed']}" title="${lang.strings['speed']}" src="images/speed_dark.svg">${lang.getLocaleSpeed(pos.speed, true)}<br>` : ''}
-        ${(pos.altitude !== null) ? `<img class="icon" alt="${lang.strings['altitude']}" title="${lang.strings['altitude']}" src="images/altitude_dark.svg">${lang.getLocaleAltitude(pos.altitude, true)}<br>` : ''}
-        ${(pos.accuracy !== null) ? `<img class="icon" alt="${lang.strings['accuracy']}" title="${lang.strings['accuracy']}" src="images/accuracy_dark.svg">${lang.getLocaleAccuracy(pos.accuracy, true)}${provider}<br>` : ''}
+        <img class="icon" alt="${$._('time')}" title="${$._('time')}" src="images/calendar_dark.svg"> ${date}<br>
+        <img class="icon" alt="${$._('time')}" title="${$._('time')}" src="images/clock_dark.svg"> ${time}<br>
+        ${(pos.speed !== null) ? `<img class="icon" alt="${$._('speed')}" title="${$._('speed')}" src="images/speed_dark.svg">${$.getLocaleSpeed(pos.speed, true)}<br>` : ''}
+        ${(pos.altitude !== null) ? `<img class="icon" alt="${$._('altitude')}" title="${$._('altitude')}" src="images/altitude_dark.svg">${$.getLocaleAltitude(pos.altitude, true)}<br>` : ''}
+        ${(pos.accuracy !== null) ? `<img class="icon" alt="${$._('accuracy')}" title="${$._('accuracy')}" src="images/accuracy_dark.svg">${$.getLocaleAccuracy(pos.accuracy, true)}${provider}<br>` : ''}
         </div>${stats}</div>
-        <div id="pfooter">${uUtils.sprintf(lang.strings['pointof'], id + 1, count)}</div>
+        <div id="pfooter">${uUtils.sprintf($._('pointof'), id + 1, count)}</div>
         </div>`;
   }
 
diff --git a/js/src/trackviewmodel.js b/js/src/trackviewmodel.js
index 71b7908..1d4e02b 100644
--- a/js/src/trackviewmodel.js
+++ b/js/src/trackviewmodel.js
@@ -17,7 +17,7 @@
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
-import { config, lang } from './initializer.js';
+import { lang as $, config } from './initializer.js';
 import ViewModel from './viewmodel.js';
 import uObserve from './observe.js';
 import uPositionSet from './positionset.js';
@@ -154,20 +154,20 @@ export default class TrackViewModel extends ViewModel {
     const form = this.importEl.parentElement;
     const sizeMax = form.elements['MAX_FILE_SIZE'].value;
     if (this.importEl.files && this.importEl.files.length === 1 && this.importEl.files[0].size > sizeMax) {
-      uUtils.error(uUtils.sprintf(lang.strings['isizefailure'], sizeMax));
+      uUtils.error(uUtils.sprintf($._('isizefailure'), sizeMax));
       return;
     }
     uTrack.import(form)
       .then((trackList) => {
         if (trackList.length) {
           if (trackList.length > 1) {
-            alert(uUtils.sprintf(lang.strings['imultiple'], trackList.length));
+            alert(uUtils.sprintf($._('imultiple'), trackList.length));
           }
           this.model.trackList = trackList.concat(this.model.trackList);
           this.model.currentTrackId = trackList[0].listValue;
         }
       })
-      .catch((e) => uUtils.error(e, `${lang.strings['actionfailure']}\n${e.message}`))
+      .catch((e) => uUtils.error(e, `${$._('actionfailure')}\n${e.message}`))
       .finally(() => {
         this.model.inputFile = '';
       });
@@ -190,7 +190,7 @@ export default class TrackViewModel extends ViewModel {
           this.model.showLatest = false;
         }
       })
-        .catch((e) => { uUtils.error(e, `${lang.strings['actionfailure']}\n${e.message}`); });
+        .catch((e) => { uUtils.error(e, `${$._('actionfailure')}\n${e.message}`); });
     }
   }
 
@@ -203,7 +203,7 @@ export default class TrackViewModel extends ViewModel {
       this.state.currentTrack.clear();
     }
     this.state.currentTrack.fetchPositions()
-      .catch((e) => { uUtils.error(e, `${lang.strings['actionfailure']}\n${e.message}`); });
+      .catch((e) => { uUtils.error(e, `${$._('actionfailure')}\n${e.message}`); });
   }
 
   /**
@@ -220,7 +220,7 @@ export default class TrackViewModel extends ViewModel {
           this.model.currentTrackId = _track.listValue;
         }
       })
-      .catch((e) => { uUtils.error(e, `${lang.strings['actionfailure']}\n${e.message}`); });
+      .catch((e) => { uUtils.error(e, `${$._('actionfailure')}\n${e.message}`); });
   }
 
   /**
@@ -235,7 +235,7 @@ export default class TrackViewModel extends ViewModel {
           this.state.currentTrack = _track;
         }
       })
-      .catch((e) => { uUtils.error(e, `${lang.strings['actionfailure']}\n${e.message}`); });
+      .catch((e) => { uUtils.error(e, `${$._('actionfailure')}\n${e.message}`); });
   }
 
   loadTrackList() {
@@ -253,7 +253,7 @@ export default class TrackViewModel extends ViewModel {
           this.model.currentTrackId = '';
         }
       })
-      .catch((e) => { uUtils.error(e, `${lang.strings['actionfailure']}\n${e.message}`); });
+      .catch((e) => { uUtils.error(e, `${$._('actionfailure')}\n${e.message}`); });
   }
 
   /**
@@ -291,14 +291,14 @@ export default class TrackViewModel extends ViewModel {
       const dateString = (date.toDateString() !== today.toDateString()) ? `${dateTime.date}<br>` : '';
       const timeString = `${dateTime.time}<span style="font-weight:normal">${dateTime.zone}</span>`;
       this.model.summary = `
-        <div class="menu-title">${lang.strings['latest']}:</div>
+        <div class="menu-title">${$._('latest')}:</div>
         ${dateString}
         ${timeString}`;
     } else {
       this.model.summary = `
-        <div class="menu-title">${lang.strings['summary']}</div>
-        <div><img class="icon" alt="${lang.strings['tdistance']}" title="${lang.strings['tdistance']}" src="images/distance.svg"> ${lang.getLocaleDistanceMajor(last.totalMeters, true)}</div>
-        <div><img class="icon" alt="${lang.strings['ttime']}" title="${lang.strings['ttime']}" src="images/time.svg"> ${lang.getLocaleDuration(last.totalSeconds)}</div>`;
+        <div class="menu-title">${$._('summary')}</div>
+        <div><img class="icon" alt="${$._('tdistance')}" title="${$._('tdistance')}" src="images/distance.svg"> ${$.getLocaleDistanceMajor(last.totalMeters, true)}</div>
+        <div><img class="icon" alt="${$._('ttime')}" title="${$._('ttime')}" src="images/time.svg"> ${$.getLocaleDuration(last.totalSeconds)}</div>`;
     }
   }
 
diff --git a/js/src/userviewmodel.js b/js/src/userviewmodel.js
index 643ff40..e5de8ea 100644
--- a/js/src/userviewmodel.js
+++ b/js/src/userviewmodel.js
@@ -17,7 +17,7 @@
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
-import { auth, lang } from './initializer.js';
+import { lang as $, auth } from './initializer.js';
 import ViewModel from './viewmodel.js';
 import uSelect from './select.js';
 import uUser from './user.js';
@@ -40,7 +40,7 @@ export default class UserViewModel extends ViewModel {
     });
     /** @type HTMLSelectElement */
     const listEl = document.querySelector('#user');
-    this.select = new uSelect(listEl, lang.strings['suser'], `- ${lang.strings['allusers']} -`);
+    this.select = new uSelect(listEl, $._('suser'), `- ${$._('allusers')} -`);
     this.state = state;
   }
 
@@ -61,7 +61,7 @@ export default class UserViewModel extends ViewModel {
         this.model.currentUserId = userId;
       }
     })
-      .catch((e) => { uUtils.error(e, `${lang.strings['actionfailure']}\n${e.message}`); });
+      .catch((e) => { uUtils.error(e, `${$._('actionfailure')}\n${e.message}`); });
   }
 
   /**
diff --git a/js/test/api_gmaps.test.js b/js/test/api_gmaps.test.js
index e95bf33..ad5bade 100644
--- a/js/test/api_gmaps.test.js
+++ b/js/test/api_gmaps.test.js
@@ -21,6 +21,7 @@ import * as gmStub from './googlemaps.stub.js';
 import { config, lang } from '../src/initializer.js'
 import GoogleMapsApi from '../src/mapapi/api_gmaps.js';
 import TrackFactory from './helpers/trackfactory.js';
+import uObserve from '../src/observe.js';
 import uUtils from '../src/utils.js';
 
 describe('Google Maps map API tests', () => {
@@ -45,10 +46,14 @@ describe('Google Maps map API tests', () => {
     spyOn(google.maps, 'Polyline').and.callThrough();
     spyOnProperty(GoogleMapsApi, 'loadTimeoutMs', 'get').and.returnValue(loadTimeout);
     spyOn(window, 'alert');
+    spyOn(lang, '_').and.returnValue('{placeholder}');
     gmStub.applyPrototypes();
   });
 
-  afterEach(() => gmStub.clear());
+  afterEach(() => {
+    gmStub.clear();
+    uObserve.unobserveAll(lang);
+  });
 
   it('should timeout initialization of map engine', (done) => {
     // given
@@ -124,13 +129,13 @@ describe('Google Maps map API tests', () => {
   it('should fail with authorization error', (done) => {
     // given
     spyOn(uUtils, 'loadScript').and.returnValue(Promise.resolve());
-    lang.strings['apifailure'] = 'authfailure';
+    lang._.and.returnValue('authfailure');
     // when
     api.init()
       .then(() => done.fail('resolve callback called'))
       .catch((e) => {
         // then
-        expect(e.message).toContain(lang.strings['apifailure']);
+        expect(e.message).toContain('authfailure');
         done();
       });
     window.gm_authFailure();
@@ -139,7 +144,7 @@ describe('Google Maps map API tests', () => {
   it('should show alert if authorization error occurs after initialization', (done) => {
     // given
     spyOn(uUtils, 'loadScript').and.returnValue(Promise.resolve());
-    lang.strings['apifailure'] = 'authfailure';
+    lang._.and.returnValue('authfailure');
     // when
     api.init()
       .then(() => {
@@ -151,7 +156,7 @@ describe('Google Maps map API tests', () => {
     window.gm_authFailure();
 
     expect(window.alert).toHaveBeenCalledTimes(1);
-    expect(window.alert.calls.mostRecent().args[0]).toContain(lang.strings['apifailure']);
+    expect(window.alert.calls.mostRecent().args[0]).toContain('authfailure');
   });
 
   it('should clean up class fields', () => {
diff --git a/js/test/chartviewmodel.test.js b/js/test/chartviewmodel.test.js
index b9483a9..e2a245b 100644
--- a/js/test/chartviewmodel.test.js
+++ b/js/test/chartviewmodel.test.js
@@ -86,6 +86,7 @@ describe('ChartViewModel tests', () => {
     state = new uState();
     vm = new ChartViewModel(state);
     spyOn(lang, 'unit');
+    spyOn(lang, '_').and.returnValue('{placeholder}');
     mockChart = jasmine.createSpyObj('mockChart', {
       'on': { /* ignored */ },
       'update': { /* ignored */ }
diff --git a/js/test/configviewmodel.test.js b/js/test/configviewmodel.test.js
index d5198a0..15d9faa 100644
--- a/js/test/configviewmodel.test.js
+++ b/js/test/configviewmodel.test.js
@@ -17,9 +17,10 @@
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
+import { config, lang } from '../src/initializer.js';
 import ConfigViewModel from '../src/configviewmodel.js';
 import ViewModel from '../src/viewmodel.js';
-import { config } from '../src/initializer.js';
+import uObserve from '../src/observe.js';
 import uState from '../src/state.js';
 import uUtils from '../src/utils.js';
 
@@ -87,10 +88,12 @@ describe('ConfigViewModel tests', () => {
     vm.init();
     spyOn(uUtils, 'setCookie').and.returnValue(newInterval);
     spyOn(ConfigViewModel, 'reload');
+    spyOn(lang, '_').and.returnValue('{placeholder}');
   });
 
   afterEach(() => {
     document.body.removeChild(document.querySelector('#fixture'));
+    uObserve.unobserveAll(lang);
   });
 
   it('should create instance with state as parameter', () => {
diff --git a/js/test/lang.test.js b/js/test/lang.test.js
new file mode 100644
index 0000000..d68fd12
--- /dev/null
+++ b/js/test/lang.test.js
@@ -0,0 +1,167 @@
+/*
+ * μlogger
+ *
+ * Copyright(C) 2019 Bartek Fabiszewski (www.fabiszewski.net)
+ *
+ * This is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+import uLang from '../src/lang.js';
+
+describe('Lang tests', () => {
+
+  let lang;
+  let mockConfig;
+  let mockStrings;
+  const value = 1000;
+
+  beforeEach(() => {
+    lang = new uLang();
+    mockConfig = {
+      factorSpeed: 0.33,
+      unitSpeed: 'units',
+      factorDistance: 1.3,
+      unitDistance: 'unitd',
+      factorDistanceMajor: 0.55,
+      unitDistanceMajor: 'unitdm',
+      unitDay: 'unitday'
+    };
+    mockStrings = {
+      string1: 'łańcuch1',
+      units: 'jp',
+      unitd: 'jo',
+      unitdm: 'jo / 1000',
+      unitday: 'd'
+    }
+  });
+
+  it('should create instance', () => {
+    expect(lang.strings).toEqual({});
+    expect(lang.config).toBe(null);
+  });
+
+  it('should initialize', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.strings).toBe(mockStrings);
+    expect(lang.config).toBe(mockConfig);
+  });
+
+  it('should return localized string', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang._('string1')).toBe(mockStrings.string1);
+  });
+
+  it('should throw error on unknown string', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(() => lang._('unknown_string')).toThrowError(/Unknown/);
+  });
+
+  it('should return localized unit', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.unit('unitSpeed')).toBe(mockStrings.units);
+  });
+
+  it('should return localized speed value', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.getLocaleSpeed(value, false)).toBe(1188);
+  });
+
+  it('should return localized speed value with unit', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.getLocaleSpeed(value, true)).toBe(`1188 ${mockStrings.units}`);
+  });
+
+  it('should return localized distance major value', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.getLocaleDistanceMajor(value, false)).toBe(0.55);
+  });
+
+  it('should return localized distance major value with unit', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.getLocaleDistanceMajor(value, true)).toBe(`0.55 ${mockStrings.unitdm}`);
+  });
+
+  it('should return localized distance value', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.getLocaleDistance(value, false)).toBe(1300);
+  });
+
+  it('should return localized distance value with unit', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.getLocaleDistance(value, true)).toBe(`1300 ${mockStrings.unitd}`);
+  });
+
+  it('should return localized altitude value', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.getLocaleDistance(value, false)).toBe(1300);
+  });
+
+  it('should return localized altitude value with unit', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.getLocaleDistance(value, true)).toBe(`1300 ${mockStrings.unitd}`);
+  });
+
+  it('should return localized accuracy value', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.getLocaleDistance(value, false)).toBe(1300);
+  });
+
+  it('should return localized accuracy value with unit', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.getLocaleDistance(value, true)).toBe(`1300 ${mockStrings.unitd}`);
+  });
+
+  it('should return localized time duration', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.getLocaleDuration(12345)).toBe('03:25:45');
+  });
+
+  it('should return localized time duration with day unit', () => {
+    // when
+    lang.init(mockConfig, mockStrings);
+    // then
+    expect(lang.getLocaleDuration(123456789)).toBe(`1428 ${mockStrings.unitday} 21:33:09`);
+  });
+
+});
diff --git a/js/test/mapviewmodel.test.js b/js/test/mapviewmodel.test.js
index 9c58ab7..b9df30e 100644
--- a/js/test/mapviewmodel.test.js
+++ b/js/test/mapviewmodel.test.js
@@ -44,7 +44,6 @@ describe('MapViewModel tests', () => {
     config.reinitialize();
     config.mapApi = defaultApi;
     lang.init(config);
-    lang.strings['apifailure'] = 'api failure: %s';
     mockApi = jasmine.createSpyObj('mockApi', {
       'init': Promise.resolve(),
       'getBounds': { /* ignored */ },
@@ -57,12 +56,17 @@ describe('MapViewModel tests', () => {
     state = new uState();
     vm = new MapViewModel(state);
     spyOn(vm, 'getApi').and.returnValue(mockApi);
+    spyOn(lang, 'getLocaleSpeed');
+    spyOn(lang, 'getLocaleDistance');
+    spyOn(lang, 'getLocaleDistanceMajor');
+    spyOn(lang, '_').and.returnValue('{placeholder}');
     bounds = [ 1, 2, 3, 4 ];
     track = TrackFactory.getTrack(0);
   });
 
   afterEach(() => {
     document.body.removeChild(document.querySelector('#fixture'));
+    uObserve.unobserveAll(lang);
   });
 
   it('should create instance', () => {
diff --git a/js/test/trackviewmodel.test.js b/js/test/trackviewmodel.test.js
index b720c53..ff7cbcc 100644
--- a/js/test/trackviewmodel.test.js
+++ b/js/test/trackviewmodel.test.js
@@ -83,6 +83,7 @@ describe('TrackViewModel tests', () => {
     config.reinitialize();
     config.interval = 10;
     lang.init(config);
+    spyOn(lang, '_').and.returnValue('{placeholder}');
     trackEl = document.querySelector('#track');
     summaryEl = document.querySelector('#summary');
     latestEl = document.querySelector('#latest');
@@ -106,6 +107,7 @@ describe('TrackViewModel tests', () => {
 
   afterEach(() => {
     document.body.removeChild(document.querySelector('#fixture'));
+    uObserve.unobserveAll(lang);
   });
 
   it('should create instance with state as parameter', () => {