[FIX] l10n_multilang: translate accounts after the installation of a CoA

Before this commit, the only way to translate a chart of account was to install
the language (if present in 'spoken_language' field on the chart of account
configuration) **before** the installation of the chart of account.

This commit loads the translations of the chart of account at the installation
of the language too.

To avoid recreating translations at each update of a language, skip if the
language is already installed.
This means than, to benefit from the fix, already deployed instances should
remove (after de-activating it) the language and reinstall it to translate
existing chart of account.

opw-670327

Closes #11091

addons/l10n_multilang/l10n_multilang.py

@@ -84,3 +84,32 @@ class AccountChartTemplate(models.Model):
         in_ids = self.env['account.fiscal.position.template'].search([('chart_template_id', '=', self.id)], order='id')
         out_ids = self.env['account.fiscal.position'].search([('company_id', '=', company_id)], order='id')
         return self.process_translations(langs, field, in_ids, out_ids)
+
+
+class base_language_install(models.TransientModel):
+    """ Install Language"""
+
+    _inherit = "base.language.install"
+
+    @api.multi
+    def lang_install(self):
+        self.ensure_one()
+        already_installed = self.env['res.lang'].search_count([('code', '=', self.lang)])
+        res = super(base_language_install, self).lang_install()
+        if already_installed:
+            # update of translations instead of new installation
+            # skip to avoid duplicating the translations
+            return res
+
+        # CoA in multilang mode
+        for coa in self.env['account.chart.template'].search([('spoken_languages', '!=', False)]):
+            if self.lang in coa.spoken_languages.split(';'):
+                # companies on which it is installed
+                for company in self.env['res.company'].search([('chart_template_id', '=', coa.id)]):
+                    # write account.account translations in the real COA
+                    coa._process_accounts_translations(company.id, [self.lang], 'name')
+                    # copy account.tax translations
+                    coa._process_taxes_translations(company.id, [self.lang], 'name')
+                    # copy account.fiscal.position translations
+                    coa._process_fiscal_pos_translations(company.id, [self.lang], 'name')
+        return res