fix(merge-pdf): route result notifications through i18n

Fixes #825

src/tests/merge-pdf-i18n.test.ts

@@ -0,0 +1,70 @@
+import { readFileSync } from 'node:fs';
+import { join } from 'node:path';
+import { describe, expect, it } from 'vitest';
+
+const ROOT = process.cwd();
+const LOGIC_FILE = join(ROOT, 'src/js/logic/merge-pdf-page.ts');
+const CHECKED_LANGUAGES = ['en', 'fr'] as const;
+
+const source = readFileSync(LOGIC_FILE, 'utf8');
+
+const loadLocale = (lang: string, namespace: 'common' | 'tools') =>
+  JSON.parse(
+    readFileSync(
+      join(ROOT, 'public/locales', lang, `${namespace}.json`),
+      'utf8'
+    )
+  ) as Record<string, unknown>;
+
+const resolveKey = (bundle: Record<string, unknown>, key: string): unknown =>
+  key
+    .split('.')
+    .reduce<unknown>(
+      (node, part) =>
+        node && typeof node === 'object'
+          ? (node as Record<string, unknown>)[part]
+          : undefined,
+      bundle
+    );
+
+const usedKeys = [...source.matchAll(/\bt\('([^']+)'/g)].map(
+  (match) => match[1]
+);
+
+describe('merge PDF notifications are localized', () => {
+  it('uses translation keys for every alert and loader message', () => {
+    const literalCalls = [
+      ...source.matchAll(/\bshow(?:Alert|Loader)\(\s*['"`]/g),
+    ];
+    expect(literalCalls).toHaveLength(0);
+  });
+
+  it('references at least the alert and loader keys added for the merge tool', () => {
+    expect(usedKeys).toContain('tools:mergePdf.alert.mergeSuccess');
+    expect(usedKeys).toContain('tools:mergePdf.loader.merging');
+    expect(usedKeys).toContain('common.success');
+    expect(usedKeys).toContain('common.error');
+  });
+
+  for (const lang of CHECKED_LANGUAGES) {
+    it(`resolves every key used by the merge tool in "${lang}"`, () => {
+      const bundles = {
+        common: loadLocale(lang, 'common'),
+        tools: loadLocale(lang, 'tools'),
+      };
+
+      const missing = usedKeys.filter((key) => {
+        const [namespace, plainKey] = key.startsWith('tools:')
+          ? ['tools', key.slice('tools:'.length)]
+          : ['common', key];
+        const value = resolveKey(
+          bundles[namespace as 'common' | 'tools'],
+          plainKey
+        );
+        return typeof value !== 'string' || value.length === 0;
+      });
+
+      expect(missing).toEqual([]);
+    });
+  }
+});