[IMP] web: prefetch translations to speed up webclient startup

closes odoo-dev/odoo#901

Signed-off-by: Géry Debongnie (ged) <ged@openerp.com>

addons/web/views/webclient_templates.xml

@@ -290,6 +290,13 @@
                     odoo.reloadMenus = () => fetch(`/web/webclient/load_menus/${odoo.session_info.cache_hashes.load_menus}`).then(res => res.json());
                     odoo.loadMenusPromise = odoo.reloadMenus();
                     odoo.loadTemplatesPromise = fetch(`/web/webclient/qweb/${odoo.session_info.cache_hashes.qweb}?bundle=web.assets_qweb`).then(doc => doc.text());
+                    // Block to avoid leaking variables in the script scope
+                    {
+                        const { user_context,  cache_hashes } = odoo.session_info;
+                        // Prefetch translations to speedup webclient. This is done in JS because link rel="prefetch"
+                        // is not yet supported on safari.
+                        fetch(`/web/webclient/translations/${cache_hashes.translations}?lang=${user_context.lang}`);
+                    }
                 </script>
                 <t t-call-assets="web.assets_common" t-js="false"/>
                 <t t-call-assets="web.assets_backend" t-js="false"/>