feat: localizations

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

core/lib/L10N/LocaleResolver.php

@@ -0,0 +1,71 @@
+<?php
+
+namespace KTXC\L10N;
+
+use DI\Attribute\Inject;
+use KTXC\Http\Request\Request;
+use KTXC\Service\UserAccountsService;
+
+/**
+ * Resolves the effective UI locale for the current user.
+ *
+ * Resolution chain: user setting (core.locale) -> Accept-Language
+ * negotiation -> fallback. Tenant default slots in between once tenant
+ * settings expose one (Phase 3).
+ */
+class LocaleResolver
+{
+    public const FALLBACK = 'en';
+    public const SETTING_KEY = 'core.locale';
+
+    public function __construct(
+        private readonly UserAccountsService $userService,
+        #[Inject('rootDir')] private readonly string $rootDir,
+    ) {}
+
+    /**
+     * Locales with a core catalog on disk (public/l10n/*.json), always
+     * including the fallback. This backs the language picker, so a locale
+     * is only offered when it has at least core-shell coverage.
+     *
+     * @return string[]
+     */
+    public function available(): array
+    {
+        $locales = [self::FALLBACK];
+        foreach (glob($this->rootDir . '/public/l10n/*.json') ?: [] as $file) {
+            $locales[] = basename($file, '.json');
+        }
+        $locales = array_values(array_unique($locales));
+        sort($locales);
+        return $locales;
+    }
+
+    public function resolve(Request $request): string
+    {
+        $available = $this->available();
+
+        // 1. explicit user preference
+        $settings = $this->userService->fetchSettings([self::SETTING_KEY]);
+        $preference = $settings[self::SETTING_KEY] ?? null;
+        if (is_string($preference) && in_array($preference, $available, true)) {
+            return $preference;
+        }
+
+        // 2. Accept-Language negotiation. getPreferredLanguage() returns the
+        // first candidate when nothing matches, so the fallback leads the
+        // list; it also normalizes to underscore form (pt_BR) while catalogs
+        // use BCP-47 hyphens.
+        $candidates = array_merge([self::FALLBACK], array_diff($available, [self::FALLBACK]));
+        $negotiated = $request->getPreferredLanguage($candidates);
+        if ($negotiated !== null) {
+            $negotiated = str_replace('_', '-', $negotiated);
+            if (in_array($negotiated, $available, true)) {
+                return $negotiated;
+            }
+        }
+
+        // 3. fallback
+        return self::FALLBACK;
+    }
+}