feedback5: merge W5I — real i18n phase 1: shared/i18n.js (Chinese msgids, params, data names), English game texts from the official EN client data (data/i18n/en.json), the 中文 / English switch on the title screen and in 设置, title / lobby / room / settings converted, server toasts and ticker lines with msgid + params, tools/i18n.mjs, docs/I18N.md (PR #70's translations by @YuriRestia reused, credited)

Conflict: server/match/player/basics.js imports (W5G's checkNotOwned + W5I's msg / dn). data/i18n/en.json rebuilt on the merged data (tools/build-i18n.mjs --offline): the 自选 data adds texts of CN-only operators and modules the EN client lacks, so coverage is 97.6 % (skills 95.9, talents 95.1); the coverage floors in test/i18n-data.test.js and docs/I18N.md say so. Golden unchanged; i18n / lobby / match / ui suites 1144/1144 after the rebuild, i18n e2e 1/1.

test/ui/i18n.e2e.test.js

@@ -0,0 +1,72 @@
+// Browser check of the language switch (puppeteer-core + system Chrome; opt-in: SP_E2E=1, ~20 s):
+//
+//   SP_E2E=1 node --test test/ui/i18n.e2e.test.js
+//
+// The title screen opens in Chinese; 中文 | English → English in place (no reload): the title, the start button, the
+// connection line, <html lang>, the tab title; the choice is kept across a reload (localStorage sp.pref.lang) and the
+// game-data overlay (data/i18n/en.json) is applied; `?lang=zh` switches back and leaves the address bar. No console /
+// page / request errors. docs/I18N.md.
+
+import { test, describe, before, after } from 'node:test';
+import assert from 'node:assert/strict';
+import { CHROME, hasChrome, sleep } from '../e2e/client.mjs';
+import { NAME_MAX_LEN } from '../../shared/constants.js';
+
+const ENABLED = process.env.SP_E2E === '1' && hasChrome();
+
+describe('language switch on the title screen', { skip: !ENABLED && 'set SP_E2E=1 (Chrome)' }, () => {
+  let srv;
+  let browser;
+  let base;
+  before(async () => {
+    const { startServer } = await import('../../server/index.js');
+    const puppeteer = (await import('puppeteer-core')).default;
+    srv = await startServer({ port: 0, host: '127.0.0.1', quiet: true });
+    base = `http://127.0.0.1:${srv.port}`;
+    browser = await puppeteer.launch({ executablePath: CHROME, headless: true, args: ['--no-sandbox', '--force-device-scale-factor=1'] });
+  });
+  after(async () => { await browser?.close(); await srv?.close(); });
+
+  const text = (page, sel) => page.$eval(sel, (el) => el.textContent.replace(/\s+/g, ' ').trim());
+
+  test('中文 by default; English in place, kept across a reload; ?lang=zh back to Chinese', async () => {
+    const page = await browser.newPage();
+    await page.setViewport({ width: 1600, height: 900 });
+    const problems = [];
+    page.on('console', (m) => { if (m.type() === 'error') problems.push(`console: ${m.text()}`); });
+    page.on('pageerror', (e) => problems.push(`pageerror: ${e.message}`));
+    page.on('response', (r) => { if (r.status() >= 400 && !/fonts\.(googleapis|gstatic)/.test(r.url())) problems.push(`http ${r.status()}: ${r.url()}`); });
+    await page.goto(`${base}/`, { waitUntil: 'networkidle0' });
+    await page.waitForSelector('.title-screen [data-testid="lang-toggle"]');
+    assert.equal(await text(page, '.title-cn'), '卫戍协议：盟约');
+    assert.equal(await text(page, '.title-login .btn--primary'), '开始');
+    assert.equal(await page.evaluate(() => document.documentElement.lang), 'zh-CN');
+
+    await page.click('[data-testid="lang-toggle"] button[data-lang="en"]');
+    await page.waitForFunction(() => document.querySelector('.title-cn')?.textContent.includes('Stronghold Protocol'), { timeout: 8000 });
+    assert.equal(await text(page, '.title-cn'), 'Stronghold Protocol: Alliance');
+    assert.equal(await text(page, '.title-login .btn--primary'), 'Start');
+    assert.match(await text(page, '.title-tag'), /^Allocate Funds and Operators/);
+    assert.match(await text(page, '.title-conn'), /Connect|Ready to connect/);
+    assert.equal(await page.$eval('.title-login input', (el) => el.placeholder), `Callsign (max ${NAME_MAX_LEN} chars)`);
+    assert.deepEqual(await page.evaluate(() => ({ lang: document.documentElement.lang, title: document.title, pref: localStorage.getItem('sp.pref.lang') })),
+      { lang: 'en', title: 'Stronghold Protocol: Alliance · Web Simulation', pref: '"en"' });
+    // the game texts follow (data/i18n/en.json applied by data.js)
+    await page.waitForFunction(() => globalThis.__SP__?.data?.locale() === 'en', { timeout: 8000 });
+    assert.equal(await page.evaluate(() => globalThis.__SP__.data.get('config').modes.mode_multi_abyss.name), 'Ultimate Simulation');
+
+    await page.reload({ waitUntil: 'networkidle0' });
+    await page.waitForSelector('.title-screen .title-cn');
+    assert.equal(await text(page, '.title-cn'), 'Stronghold Protocol: Alliance', 'the choice survives a reload');
+    assert.equal(await text(page, '.title-login .btn--primary'), 'Start');
+
+    await page.goto(`${base}/?lang=zh`, { waitUntil: 'networkidle0' });
+    await page.waitForSelector('.title-screen .title-cn');
+    await sleep(200);
+    assert.equal(await text(page, '.title-cn'), '卫戍协议：盟约');
+    assert.equal(await page.evaluate(() => location.search), '', '?lang is removed from the address bar');
+    assert.equal(await page.evaluate(() => localStorage.getItem('sp.pref.lang')), '"zh"');
+    assert.deepEqual(problems, []);
+    await page.close();
+  });
+});