[FIX] l10n_de: DATEV export compatiblity

When invoicing a line with an account that has a tax, ensure that line has the same tax of accounts. This is required by DATEV and is common usage in Germany

Was task 35289
Was PR #25202

addons/l10n_de/models/datev.py

@@ -1,4 +1,6 @@
-from odoo import fields, models
+from odoo import api, fields, models
+from odoo.exceptions import UserError
+from odoo.tools.translate import _
 
 class AccountTaxTemplate(models.Model):
     _inherit = 'account.tax.template'
@@ -14,3 +16,18 @@ class AccountTax(models.Model):
     _inherit = "account.tax"
 
     l10n_de_datev_code = fields.Char(size=2, help="2 digits code use by Datev")
+
+class AccountInvoice(models.Model):
+    _inherit = "account.invoice"
+
+    def invoice_validate(self):
+        for invoice in self:
+            for line in invoice.invoice_line_ids:
+                account_tax = line.account_id.tax_ids.ids
+                if account_tax and invoice.company_id.country_id.code == 'DE':
+                    account_name = line.account_id.name
+                    for tax in line.invoice_line_tax_ids:
+                        if tax.id not in account_tax:
+                            raise UserError(_('Account %s does not authorize to have tax %s specified on the line. \
+                                Change the tax used in this invoice or remove all taxes from the account') % (account_name, tax.name))
+        return super(AccountInvoice, self).invoice_validate()