[FIX] point_of_sale: set default language for new customers

Previously, when creating a new customer from the POS interface, if
the default language was not changed in the form, an empty string
would be sent to the backend. This resulted in the new customer not
having a language set.

This commit establishes the default language selection as the user's
selected language when creating a new customer within the POS system.

opw-3466525

closes odoo/odoo#133020

Signed-off-by: Joseph Caburnay (jcb) <jcb@odoo.com>

addons/point_of_sale/static/src/js/Screens/PartnerListScreen/PartnerListScreen.js

@@ -8,6 +8,7 @@ odoo.define('point_of_sale.PartnerListScreen', function(require) {
     const { debounce } = require("@web/core/utils/timing");
     const { useListener } = require("@web/core/utils/hooks");
     const { useAsyncLockedMethod } = require("point_of_sale.custom_hooks");
+    const { session } = require("@web/session");
 
     const { onWillUnmount, useRef } = owl;
 
@@ -151,10 +152,11 @@ odoo.define('point_of_sale.PartnerListScreen', function(require) {
             this.activateEditMode();
         }
         createPartner() {
-            // initialize the edit screen with default details about country & state
+            // initialize the edit screen with default details about country, state & lang
             this.state.editModeProps.partner = {
                 country_id: this.env.pos.company.country_id,
                 state_id: this.env.pos.company.state_id,
+                lang: session.user_context.lang,
             }
             this.activateEditMode();
         }