[FIX] web: load_translation fallback to url language

This commit is fine tuning of 9f142c8ff5a383.

Apparently, context_get callback is never called. I
guess this is due to the fact that we are higher.

context_get is defined in public/public_root.js and
we are in core/session.js

The only way to fix is to retrieve the HTML tag language.

OPW-2244843

closes odoo/odoo#53155

X-original-commit: 2bbb8fbf7ae909da03d97d16b228ae5a95de7d18
Signed-off-by: Jason Van Malder (jvm) <jvm@odoo.com>

addons/web/static/src/js/core/session.js

@@ -211,15 +211,13 @@ var Session = core.Class.extend(mixins.EventDispatcherMixin, {
         });
     },
     load_translations: function () {
-        var lang = this.user_context.lang;
-
-        if (!lang) {
-            this.trigger_up('context_get', {
-                callback: function (ctx) {
-                    lang = ctx.lang;
-                },
-            });
-        }
+        /* We need to get the website lang at this level.
+           The only way is to get it is to take the HTML tag lang
+           Without it, we will always send undefined if there is no lang
+           in the user_context. */
+        var html = document.documentElement,
+            htmlLang = (html.getAttribute('lang') || 'en_US').replace('-', '_'),
+            lang = this.user_context.lang || htmlLang;
 
         return _t.database.load_translations(this, this.module_list, lang, this.translationURL);
     },