[FIX] crm: default partner lang

- Create a lead and set a language
- Convert to opportunity and choose 'Create a new customer'

The new customer created doesn't have the language of the lead set.

This is more logical to set the same language to the new customer.

opw-2270321

closes odoo/odoo#52376

X-original-commit: 1999c68ff4eb382019c92064d9285411314a39be
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>