i18n: BCP-47 URL locales + complete EN translations

- URL surface now matches Angular: `/ru-ru/`, `/en-us/`, `/zh-cn/`, …
  (BCP-47). Bare short codes still work — the [lang]/layout auto-
  promotes them with a replace navigation. Internally everything that
  needs the short language (i18n file lookup, API path segment,
  Accept-Language header, dictionary `title[lang]` key, Intl
  formatters) reads it through the new `useLocale()` hook, which
  returns both `locale` (BCP-47) and `language` (short).
- ApiClient.locale is now mutable and is updated from the [lang]
  layout whenever the URL locale changes — was hard-coded to "ru" in
  the root layout before, so backend responses for /en/... still came
  back in Russian. Cities / airports / flight statuses now arrive in
  the active language.
- All 21 empty EN translation keys filled in (AIRPLANE.*, BOARD.
  PREVIOUS-FLIGHT, SCHEDULE.FILE-NAME, SEO.SCHEDULE.*, SEO.FLIGHTS-
  MAP.*, SHARED.FLIGHT-TRANSFER-PLURAL-*, SHARED.WEEK_FORMAT-WRONG)
  so /en-us renders without falling back to raw keys.
- Added BOARD.LOAD-FAILED-TITLE / -MESSAGE keys (RU + EN) and removed
  the three hardcoded Russian error strings from the search-page
  error card.
- FlightStatus now reads `FLIGHT-STATUSES.{Status}` from i18n instead
  of hardcoding the Russian labels.
- FlightCard's OperatorLogo now picks the en/ru carrier-logo variant
  from `useLocale().language` instead of always passing "ru" — the
  Aeroflot/Rossiya logos display in the active language where
  variants exist.
- registerPrimeLocales(): all 9 supported languages get a PrimeReact
  `addLocale` entry at module load (RU + EN hand-curated, others built
  from Intl). Calendar/AutoComplete widgets switch with the URL.
- ErrorBoundary catches outside the i18n provider, so it now ships
  its own minimal localised string table keyed off the URL locale —
  no more "Something went wrong" leaking on the Russian site.
- Hreflang URLs now emit BCP-47 (`/en-us/...`) while `hreflang="en"`
  stays the short Google-friendly form.
- Datetime helpers accept either short or BCP-47 locale (`isRussianLocale`)
  so callers can pass through whatever the route hands them.

src/ui/errors/ErrorBoundary.test.tsx

@@ -34,7 +34,9 @@ describe("ErrorBoundary", () => {
     );
     expect(getByRole("alert")).toBeDefined();
     expect(getByText("boom")).toBeDefined();
-    expect(getByText("Retry")).toBeDefined();
+    // jsdom defaults to a non-locale path, so the boundary falls back
+    // to the default app language (ru).
+    expect(getByText("Повторить")).toBeDefined();
   });
 
   it("shows custom fallback when provided", () => {
@@ -64,7 +66,7 @@ describe("ErrorBoundary", () => {
 
     // Stop throwing before retry
     shouldThrow = false;
-    fireEvent.click(getByText("Retry"));
+    fireEvent.click(getByText("Повторить"));
 
     expect(getByText("recovered")).toBeDefined();
   });

src/ui/errors/ErrorBoundary.tsx

@@ -1,5 +1,6 @@
 import { Component } from "react";
 import type { ReactNode, ErrorInfo } from "react";
+import { resolveLocaleFromPath, localeToLanguage } from "@/i18n/resolver.js";
 
 export interface ErrorBoundaryProps {
   children: ReactNode;
@@ -11,6 +12,32 @@ interface ErrorBoundaryState {
   error: Error | null;
 }
 
+/**
+ * Hand-rolled localised strings for the boundary. We can't call
+ * `useTranslation()` here (class component, AND the i18n provider may
+ * not exist when the error fires), so we read the locale from the URL
+ * and fall back to English for any language we don't have coverage
+ * for. Mirrors what Angular's global ErrorHandler renders.
+ */
+const FALLBACK_STRINGS: Record<string, { title: string; retry: string }> = {
+  ru: { title: "Что-то пошло не так", retry: "Повторить" },
+  en: { title: "Something went wrong", retry: "Retry" },
+  es: { title: "Algo salió mal", retry: "Reintentar" },
+  fr: { title: "Une erreur s'est produite", retry: "Réessayer" },
+  it: { title: "Qualcosa è andato storto", retry: "Riprova" },
+  de: { title: "Etwas ist schiefgelaufen", retry: "Wiederholen" },
+  ja: { title: "問題が発生しました", retry: "再試行" },
+  ko: { title: "문제가 발생했습니다", retry: "다시 시도" },
+  zh: { title: "出错了", retry: "重试" },
+};
+
+function pickStrings(): { title: string; retry: string } {
+  if (typeof window === "undefined") return FALLBACK_STRINGS.ru!;
+  const locale = resolveLocaleFromPath(window.location.pathname);
+  const lang = locale ? localeToLanguage(locale) : "ru";
+  return FALLBACK_STRINGS[lang] ?? FALLBACK_STRINGS.en!;
+}
+
 /**
  * React error boundary that catches render-time exceptions in the subtree.
  * Displays a minimal fallback UI with a "Retry" button that resets state.
@@ -40,12 +67,13 @@ export class ErrorBoundary extends Component<ErrorBoundaryProps, ErrorBoundarySt
         return this.props.fallback;
       }
 
+      const strings = pickStrings();
       return (
         <div role="alert">
-          <h2>Something went wrong</h2>
+          <h2>{strings.title}</h2>
           <p>{this.state.error?.message}</p>
           <button type="button" onClick={this.handleRetry}>
-            Retry
+            {strings.retry}
           </button>
         </div>
       );

src/ui/flights/FlightCard.tsx

@@ -1,5 +1,6 @@
 import { useState, type FC, type KeyboardEvent } from "react";
 import { useTranslation } from "@/i18n/provider.js";
+import { useLocale } from "@/i18n/useLocale.js";
 import type { ISimpleFlight, IFlightLeg } from "@/features/online-board/types.js";
 import { operatingCarrier } from "@/features/online-board/types.js";
 import {
@@ -76,6 +77,7 @@ export const FlightCard: FC<FlightCardProps> = ({
   onViewDetails,
 }) => {
   const { t } = useTranslation();
+  const { language } = useLocale();
   const departureLeg = getPrimaryLeg(flight);
   const arrivalLeg = getFinalLeg(flight);
 
@@ -155,7 +157,7 @@ export const FlightCard: FC<FlightCardProps> = ({
         </div>
 
         <div className="flight-card__operator">
-          <OperatorLogo carrier={carrier} locale="ru" />
+          <OperatorLogo carrier={carrier} locale={language} />
         </div>
 
         <div className="flight-card__time">

src/ui/flights/FlightStatus.tsx

@@ -1,4 +1,5 @@
 import type { FC } from "react";
+import { useTranslation } from "@/i18n/provider.js";
 import type { FlightStatus as FlightStatusType } from "@/features/online-board/types.js";
 import "./FlightStatus.scss";
 
@@ -8,17 +9,6 @@ export interface FlightStatusProps {
   withIcon?: boolean;
 }
 
-const STATUS_LABELS_RU: Record<FlightStatusType, string> = {
-  Scheduled: "Запланирован",
-  Sent: "Вылетел",
-  InFlight: "В полете",
-  Landed: "Приземлился",
-  Arrived: "Прибыл",
-  Delayed: "Задержан",
-  Cancelled: "Отменен",
-  Unknown: "—",
-};
-
 const STATUS_CLASSES: Record<FlightStatusType, string> = {
   Scheduled: "flight-status--scheduled",
   Sent: "flight-status--departed",
@@ -52,12 +42,18 @@ function statusColor(status: FlightStatusType): string {
  * into either the row header or the full details page. When `withIcon`
  * is false, degrades to a bare label (back-compat for spots that only
  * want the text badge).
+ *
+ * Status text comes from i18n (`FLIGHT-STATUSES.{status}`) so it
+ * renders in whichever locale the visitor is browsing in.
  */
 export const FlightStatus: FC<FlightStatusProps> = ({ status, withIcon = true }) => {
+  const { t } = useTranslation();
+  const label = t(`FLIGHT-STATUSES.${status}`);
+
   if (!withIcon) {
     return (
       <span className={`flight-status ${STATUS_CLASSES[status]}`}>
-        {STATUS_LABELS_RU[status]}
+        {label}
       </span>
     );
   }
@@ -75,7 +71,7 @@ export const FlightStatus: FC<FlightStatusProps> = ({ status, withIcon = true })
       >
         <path d="M21 16v-2l-8-5V3.5a1.5 1.5 0 1 0-3 0V9l-8 5v2l8-2.5V19l-2 1.5V22l3.5-1 3.5 1v-1.5L13 19v-5.5L21 16z" />
       </svg>
-      <span className="flight-status__label">{STATUS_LABELS_RU[status]}</span>
+      <span className="flight-status__label">{label}</span>
     </div>
   );
 };

src/ui/layout/PageTabs.tsx

@@ -6,8 +6,9 @@
  */
 
 import type { FC } from "react";
-import { Link, useParams } from "@modern-js/runtime/router";
+import { Link } from "@modern-js/runtime/router";
 import { useTranslation } from "@/i18n/provider.js";
+import { useLocale } from "@/i18n/useLocale.js";
 import { useFeatureFlag } from "@/features/flights-map/hooks/useFeatureFlag.js";
 import "./PageTabs.scss";
 
@@ -25,22 +26,21 @@ export const PageTabs: FC<PageTabsProps> = ({
   const flightsMapEnabled = useFeatureFlag("flightsMap");
   const showMap = showFlightsMap ?? flightsMapEnabled;
   const { t } = useTranslation();
-  const routeParams = useParams<{ lang: string }>();
-  const lang = routeParams.lang ?? "ru";
+  const { locale } = useLocale();
 
   return (
     <div className="tabs">
       <div className="tabs__row">
         <Link
           className={`tabs__tab${viewType === "onlineboard" ? " active" : ""}`}
-          to={`/${lang}/onlineboard`}
+          to={`/${locale}/onlineboard`}
           data-testid="onlineboard-tab"
         >
           {t("BOARD.TITLE")}
         </Link>
         <Link
           className={`tabs__tab${viewType === "schedule" ? " active" : ""}`}
-          to={`/${lang}/schedule`}
+          to={`/${locale}/schedule`}
           data-testid="schedule-tab"
         >
           {t("SCHEDULE.TITLE-TAB")}
@@ -51,7 +51,7 @@ export const PageTabs: FC<PageTabsProps> = ({
         <div className="tabs__row">
           <Link
             className={`tabs__tab tabs__tab--full${viewType === "flights-map" ? " active" : ""}`}
-            to={`/${lang}/flights-map`}
+            to={`/${locale}/flights-map`}
             data-testid="flights-map-tab"
           >
             {t("FLIGHTS-MAP.TITLE")}

src/ui/layout/SearchHistory.tsx

@@ -8,18 +8,18 @@
  */
 
 import { type FC, useState, useCallback } from "react";
-import { useNavigate, useParams } from "@modern-js/runtime/router";
+import { useNavigate } from "@modern-js/runtime/router";
 import { useTranslation } from "@/i18n/provider.js";
+import { useLocale } from "@/i18n/useLocale.js";
 import { useSearchHistory, type SearchHistoryItem } from "@/shared/hooks/useSearchHistory.js";
 import "./SearchHistory.scss";
 
 export const SearchHistory: FC = () => {
   const { t } = useTranslation();
   const navigate = useNavigate();
-  const routeParams = useParams<{ lang: string }>();
-  const lang = routeParams.lang ?? "ru";
+  const { language } = useLocale();
 
-  const { items } = useSearchHistory(lang);
+  const { items } = useSearchHistory(language);
   const [expanded, setExpanded] = useState(false);
 
   const handleItemClick = useCallback(