fix: address code review feedback on error messages and comments

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

packages/core/src/fallbacks/memory-i18n.ts

@@ -35,6 +35,7 @@ export function createMemoryI18n() {
       const value = data ? resolveKey(data, key) : undefined;
       if (value == null) return key;
       if (!params) return value;
+      // Interpolation format: {{paramName}} — matches FileI18nAdapter convention
       return value.replace(/\{\{(\w+)\}\}/g, (_, name) => String(params[name] ?? `{{${name}}}`));
     },
 

packages/rest/src/rest-server.ts

@@ -695,7 +695,7 @@ export class RestServer {
                         const locales = await this.protocol.getLocales({});
                         res.json(locales);
                     } else {
-                        res.status(501).json({ error: 'i18n locales not supported by protocol implementation' });
+                        res.status(501).json({ error: 'i18n service not available in protocol' });
                     }
                 } catch (error: any) {
                     res.status(500).json({ error: error.message });
@@ -717,7 +717,7 @@ export class RestServer {
                         const translations = await this.protocol.getTranslations({ locale: req.params.locale });
                         res.json(translations);
                     } else {
-                        res.status(501).json({ error: 'i18n translations not supported by protocol implementation' });
+                        res.status(501).json({ error: 'i18n service not available in protocol' });
                     }
                 } catch (error: any) {
                     res.status(500).json({ error: error.message });