Load translations for the OS language, not only the languages Chromium ships - #632

…og titles (#634)

## Why

Several modules build sentences in main and send them to the window, and
main has its own menu and native dialogs. Main had no catalog, so a
translated window would still show those in English. This is the first
batch of #622, and #625, #627, #628 and #629 need it.

## What changes

- Main resolves the locale once (`localeReply()` in `src/main.js`) and
applies it with the same `applyLocale()` the renderer uses, before it
builds the menu and the window. The `i18n:locale` handler returns that
same reply, so main and the window cannot disagree, and the en-XA
pseudo-locale now covers main too.
- Wrapped: "Open App Log" and "Show Logs Folder" in the Help menu, and
the titles and filter names of the save-patch, choose-patch and
choose-application dialogs. 10 strings.
- Electron's role menus (File, Edit, View, Window) are deliberately left
alone, as the issue says.

## How to test this

Covered by a journey, red without this change: from the repository root,
`npx playwright test --project=journeys tests/e2e/journeys/i18n.spec.js
-g "Help menu"`. It reads the Help menu labels and the title and filters
the patch file dialog was opened with, under `--lang=en-XA`.

What the journey cannot reach is the real OS dialog. Platform: Windows
for the dialogs (macOS does not show an open or save panel's title),
either for the menu. Build: the current head.

**Starting state:** the app launched from the repository root with `npx
electron . --lang=en-XA`, with one site that has an edited file.

1. Open the **Help** menu. Expected: both "Open App Log" and "Show Logs
Folder" are accented and in brackets. "Toggle Developer Tools" stays in
English (a role menu).
2. Click **Review & submit changes**, then **Save**. Expected: the save
dialog's title ("Save Diff File") and its "Patch Files" filter are
accented and in brackets.
3. Cancel. In the **Apply a patch or PR** card, open the **Diff** tab
and click **Choose a .diff or .patch file…**. Expected: the dialog title
and both filters are accented and in brackets.
4. Cancel. Open **Site actions → Open in → Other application…**.
Expected: the title and the "Programs" filter are accented and in
brackets.

**What must not have happened:** launching with no `--lang` shows every
one of these in English, and the app opens one window, not two, when
started from a `wpct://ticket/…` link.

## Risks and limitations

- Main now awaits the locale before it creates the window, so startup
gains one catalog read (the same one the window already waited for). A
`wpct://` link that arrives in that gap opens the window itself; startup
then creates a window only if none exists.
- Not tested by a journey: the save dialog and the choose-application
dialog. Only the patch file dialog is checked.
- "Dev server stopped unexpectedly (see Help → Open App Log for
details)" still names the menu entry in English. It belongs in #627,
where it should take the label as `%s`.

## Related

Fixes #623. Part of #622. Follows #632 (#584).

---

<details>
<summary>Design decisions and alternatives considered</summary>

The reply is memoised rather than computed twice so the window and main
read the catalog once and always agree. `applyLocale()` was reused as
is: it has no DOM dependency, and with main's `setLocaleData` and
`addFilter` it installs the pseudo-locale filters for main too. Main's
CommonJS `@wordpress/i18n` builds its default instance on
`@wordpress/hooks`' `defaultHooks`, and there is one copy of
`@wordpress/hooks`, so the filters apply to `menu.js` as well.

</details>

<details>
<summary>Review outcome (required, see AGENTS.md)</summary>

- **Review:** completed. Reviewer: a separate agent context (Claude
Code, read-only) against
`.github/instructions/code-review.instructions.md`; head `08d29ef` /
base `eb3f70f`. `npm run lint` clean, `npm test` 1955 pass / 0 fail,
full journey suite 114 pass. Outcome: 1 [fix here] · 1 [follow-up], both
🔵 low.
- Architecture, `src/main.js` ready path: if the locale load rejected,
startup would stop before the menu and the window. **Not changed:** the
reviewer found no path that rejects (`resolveCatalog` catches its own
read and parse errors), and AGENTS.md asks for no defensive branches
without a realistic path.
- Tests, `tests/unit/ipc-wiring.test.cjs`: the `ready` path runs after
the harness removes its require hook, so a lazy `require` added there
would load real modules. **Fixed** with a note beside the option.
- **Since review:** `08d29ef → 4c34787` checked; the only change is that
comment. Then rebased onto `trunk` after #632's squash merge: head
`a6fb7da` / base `8dbed36`. The diff against the new base is line for
line the reviewed one plus that comment; lint clean, `npm test` 1955
pass / 0 fail, journeys 114 pass on the new head.

</details>

<details>
<summary>Implementation notes</summary>

- `tests/unit/ipc-wiring.test.cjs` gains a `ready` option so one test
can run the ready path. It checks that main applies the locale before
any menu or window exists, that the handler returns the same reply
object, and that the catalog is read once.
- `tests/unit/menu.test.cjs` checks the labels are translated when the
template is built, not at require time.

</details>

<details>
<summary>Screenshots or recording</summary>

Nothing changes in English. In the pseudo-locale the change is the Help
menu labels and the native dialog titles, which the journey asserts.

</details>

🤖 Generated with [Claude Code](https://claude.com/claude-code)