Add test that the translation JSON is valid (#4315)

# Description of Changes
Adds a vitest to check that the translation JSON files exist and are
actually valid JSON.

frontend/src/tests/translation.test.ts

@@ -0,0 +1,50 @@
+import { describe, test, expect } from 'vitest';
+import fs from 'fs';
+import path from 'path';
+
+const LOCALES_DIR = path.join(__dirname, '../../public/locales');
+
+// Get all locale directories for parameterized tests
+const getLocaleDirectories = () => {
+  if (!fs.existsSync(LOCALES_DIR)) {
+    return [];
+  }
+
+  return fs.readdirSync(LOCALES_DIR, { withFileTypes: true })
+    .filter(dirent => dirent.isDirectory())
+    .map(dirent => dirent.name);
+};
+
+const localeDirectories = getLocaleDirectories();
+
+describe('Translation JSON Validation', () => {
+  test('should find the locales directory', () => {
+    expect(fs.existsSync(LOCALES_DIR)).toBe(true);
+  });
+
+  test('should have at least one locale directory', () => {
+    expect(localeDirectories.length).toBeGreaterThan(0);
+  });
+
+  test.each(localeDirectories)('should have valid JSON in %s/translation.json', (localeDir) => {
+    const translationFile = path.join(LOCALES_DIR, localeDir, 'translation.json');
+
+    // Check if file exists
+    expect(fs.existsSync(translationFile)).toBe(true);
+
+    // Read file content
+    const content = fs.readFileSync(translationFile, 'utf8');
+    expect(content.trim()).not.toBe('');
+
+    // Parse JSON - this will throw if invalid JSON
+    let jsonData;
+    expect(() => {
+      jsonData = JSON.parse(content);
+    }).not.toThrow();
+
+    // Ensure it's an object at root level
+    expect(typeof jsonData).toBe('object');
+    expect(jsonData).not.toBeNull();
+    expect(Array.isArray(jsonData)).toBe(false);
+  });
+});