Fix breadcrumb and add test for locales (#49)

* test(unit): add test to check for locale consistency

* fix(breadcrumb): translate lessons route

test/unit/locales.test.js

@@ -0,0 +1,11 @@
+const germanLocales = require('../../i18n/locales/de-DE.json')
+const englishLocales = require('../../i18n/locales/en-US.json')
+
+describe('locales', () => {
+  test('all labels coexist in all locale files', async () => {
+    const germanKeys = Object.keys(germanLocales)
+    const englishKeys = Object.keys(englishLocales)
+
+    expect(germanKeys).toEqual(englishKeys)
+  })
+})