Refactor i18n handling for language cookie and headers

The commit encompasses the aspect of refactoring the i18n handling for language cookies and headers. It also includes the deletion of get-language-cookie file and its transformation into a function inside i18n.server file. Extra functionalities were added to the i18n.server like enhancing the i18n server instance creation to consider the 'accept-language' header and default to environment provided values when necessary. The changes were also adjusted accordingly on the packages/i18n/package.json where deletion of "./cookie" was realized.

apps/web/lib/i18n/i18n.server.ts

@@ -1,10 +1,27 @@
-import getLanguageCookie from '@kit/i18n/cookie';
-import { initializeServerI18n } from '@kit/i18n/server';
+import { cookies, headers } from 'next/headers';
+
+import {
+  getLanguageCookie,
+  initializeServerI18n,
+  parseAcceptLanguageHeader,
+} from '@kit/i18n/server';
 
 import { i18nResolver } from './i18n.resolver';
 
+/**
+ * @name createI18nServerInstance
+ * @description Creates an instance of the i18n server.
+ * It uses the language from the cookie if it exists, otherwise it uses the language from the accept-language header.
+ * If neither is available, it will default to the provided environment variable.
+ *
+ * Initialize the i18n instance for every RSC server request (eg. each page/layout)
+ */
 export function createI18nServerInstance() {
-  const cookie = getLanguageCookie();
+  const acceptLanguage = headers().get('accept-language');
+  const cookie = getLanguageCookie(cookies());
 
-  return initializeServerI18n(cookie, i18nResolver);
+  const language =
+    cookie ?? parseAcceptLanguageHeader(acceptLanguage)[0] ?? undefined;
+
+  return initializeServerI18n(language, i18nResolver);
 }