feat(i18n): add reactive Alpine $t() magic and fix storefront language variable

- Register Alpine magic $t() for reactive translations in templates
- Dispatch i18n:ready event when translations load
- Fix base.html to use current_language instead of storefront_language

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

static/shared/js/i18n.js

@@ -11,9 +11,13 @@
  *   // Or load modules later
  *   await I18n.loadModule('inventory');
  *
- *   // Translate
+ *   // Translate (in JS)
  *   const message = I18n.t('catalog.messages.product_created');
  *   const withVars = I18n.t('common.welcome', { name: 'John' });
+ *
+ *   // Translate (in Alpine templates — reactive, updates when translations load)
+ *   // <span x-text="$t('catalog.messages.product_created')"></span>
+ *   // <span x-text="$t('common.welcome', {name: user})"></span>
  */
 
 // Create logger for i18n module (with silent fallback if LogConfig not yet loaded)
@@ -43,6 +47,7 @@ const I18n = {
         if (modules && modules.length > 0) {
             await Promise.all(modules.map(m => this.loadModule(m)));
         }
+        this._notifyReady();
     },
 
     /**
@@ -159,12 +164,44 @@ const I18n = {
                     await this.loadModule(module);
                 }
             }
+            this._notifyReady();
         } catch (e) {
             i18nLog.error('Failed to change language:', e);
         }
+    },
+
+    /**
+     * Notify Alpine (and other listeners) that translations are ready.
+     * Bumps the Alpine store version so reactive $t() bindings re-evaluate.
+     */
+    _notifyReady() {
+        this._ready = true;
+        // Bump Alpine store version if available (triggers $t() re-evaluation)
+        if (typeof Alpine !== 'undefined' && Alpine.store) {
+            const store = Alpine.store('i18n');
+            if (store) store._v++;
+        }
+        document.dispatchEvent(new CustomEvent('i18n:ready'));
     }
 };
 
+// Register Alpine magic $t() — reactive wrapper around I18n.t()
+// Works across all frontends (merchant, admin, store, storefront)
+document.addEventListener('alpine:init', () => {
+    // Store with a reactive version counter
+    Alpine.store('i18n', { _v: 0 });
+
+    // $t('key', {vars}) — use in x-text, x-html, or any Alpine expression
+    // Before translations load, returns the key (which matches fallback text);
+    // after _notifyReady() bumps _v, Alpine re-evaluates with loaded translations.
+    Alpine.magic('t', (el) => {
+        return (key, vars) => {
+            void Alpine.store('i18n')._v;  // reactive dependency
+            return I18n.t(key, vars);
+        };
+    });
+});
+
 // Export for module usage
 if (typeof window !== 'undefined') {
     window.I18n = I18n;