Support language code on URL in the form ?l=cy (#202)

Precedence as per classroom/Python.

Author: microbit-grace

src/__tests__/i18n.test.ts

@@ -28,6 +28,9 @@ describe('Initialization tests', () => {
       navigator: {
         languages: ['cy', 'en'],
       },
+      location: {
+        search: '',
+      },
     }));
     const i18n = await import('../i18n');
     const getText = get(i18n.t);
@@ -42,6 +45,9 @@ describe('Initialization tests', () => {
       navigator: {
         languages: ['random-language'],
       },
+      location: {
+        search: '',
+      },
     }));
     const i18n = await import('../i18n');
     const getText = get(i18n.t);
@@ -50,4 +56,21 @@ describe('Initialization tests', () => {
 
     expect(translatedText).toBe('You are currently recording!');
   });
+
+  test('Language is set to welsh when it is defined query string', async () => {
+    windowSpy.mockImplementation(() => ({
+      navigator: {
+        languages: ['some languages'],
+      },
+      location: {
+        search: '?l=cy',
+      },
+    }));
+    const i18n = await import('../i18n');
+    const getText = get(i18n.t);
+
+    const translatedText = getText('alert.isRecording');
+
+    expect(translatedText).toBe("Rydych chi'n recordio ar hyn o bryd!");
+  });
 });

src/i18n.ts

@@ -6,7 +6,7 @@
 
 import browserLang from 'browser-lang';
 import { FormatXMLElementFn } from 'intl-messageformat';
-import { init, locale, register } from 'svelte-i18n';
+import { getLocaleFromQueryString, init, locale, register } from 'svelte-i18n';
 import { get } from 'svelte/store';
 import { persistantWritable } from './script/stores/storeUtil';
 export { t } from 'svelte-i18n';
@@ -54,10 +54,12 @@ export const allLanguages = [
 register('en', () => import('./messages/ui.en.json'));
 register('cy', () => import('./messages/ui.cy.json'));
 
-const initialLocale = browserLang({
-  languages: allLanguages.map(l => l.id),
-  fallback: 'en',
-});
+const initialLocale =
+  getLocaleFromQueryString('l') ||
+  browserLang({
+    languages: allLanguages.map(l => l.id),
+    fallback: 'en',
+  });
 
 const persistantLocale = persistantWritable('lang', initialLocale);