Task/improve error handling in HTML template middleware (#7331)

* Improve error handling

* Update changelog

CHANGELOG.md

@@ -25,6 +25,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Resolved a startup error in data gathering caused by uninitialized data provider mappings
+- Improved the error handling in the `HtmlTemplateMiddleware`
 - Improved the error handling in the get quotes functionality of the _Financial Modeling Prep_ service
 
 ## 3.26.0 - 2026-07-14

apps/api/src/middlewares/html-template.middleware.ts

@@ -97,20 +97,29 @@ export class HtmlTemplateMiddleware implements NestMiddleware {
   private indexHtmlMap: { [languageCode: string]: string } = {};
 
   public constructor(private readonly i18nService: I18nService) {
-    try {
-      this.indexHtmlMap = SUPPORTED_LANGUAGE_CODES.reduce(
-        (map, languageCode) => ({
-          ...map,
-          [languageCode]: readFileSync(
-            join(__dirname, '..', 'client', languageCode, 'index.html'),
-            'utf8'
-          )
-        }),
-        {}
-      );
-    } catch (error) {
-      this.logger.error('Failed to initialize index HTML map', error);
+    if (!environment.production) {
+      return;
     }
+
+    this.indexHtmlMap = SUPPORTED_LANGUAGE_CODES.reduce((map, languageCode) => {
+      const indexHtmlPath = join(
+        __dirname,
+        '..',
+        'client',
+        languageCode,
+        'index.html'
+      );
+
+      try {
+        map[languageCode] = readFileSync(indexHtmlPath, 'utf8');
+      } catch {
+        this.logger.warn(
+          `Skipping language '${languageCode}': ${indexHtmlPath} not found`
+        );
+      }
+
+      return map;
+    }, {});
   }
 
   public use(request: Request, response: Response, next: NextFunction) {
@@ -118,7 +127,8 @@ export class HtmlTemplateMiddleware implements NestMiddleware {
     let languageCode = path.substr(1, 2);
 
     if (
-      !(SUPPORTED_LANGUAGE_CODES as readonly string[]).includes(languageCode)
+      !(SUPPORTED_LANGUAGE_CODES as readonly string[]).includes(languageCode) ||
+      !this.indexHtmlMap[languageCode]
     ) {
       languageCode = DEFAULT_LANGUAGE_CODE;
     }