[FIX] payment: do not rely on English as default language

If the database is create in monolangue and `en_US` is not present, the default
value computation crashes as tries to assign a value not present in the
selection (all installed languages).

Use the environment language as default (same as the default of res.partner).
It may be empty but not a value not existant in the database.

Fixes #15165 
Closes #15176

addons/payment/models/payment_acquirer.py

@@ -429,7 +429,7 @@ class PaymentTransaction(models.Model):
     # duplicate partner / transaction data to store the values at transaction time
     partner_id = fields.Many2one('res.partner', 'Partner', track_visibility='onchange')
     partner_name = fields.Char('Partner Name')
-    partner_lang = fields.Selection(_lang_get, 'Language', default='en_US')
+    partner_lang = fields.Selection(_lang_get, 'Language', default=lambda self: self.env.lang)
     partner_email = fields.Char('Email')
     partner_zip = fields.Char('Zip')
     partner_address = fields.Char('Address')

doc/cla/individual/daramousk.md

@@ -0,0 +1,11 @@
+Greece, 2017-01-22
+
+I hereby agree to the terms of the Odoo Individual Contributor License
+Agreement v1.0.
+
+I declare that I am authorized and able to make this agreement and sign this
+declaration.
+
+Signed,
+
+George Daramouskas george.daramouskas@gmail.com https://github.com/daramousk