[IMP] base: allow 'render' override with new api

New API use a frozendict for context, so when a function in the call
chain is overrided by new API (eg: render function of ir.qweb) the code
now changed by this commit would cause an error.

Instead this code duplicate the context frozendict as a dict removing
the need to set back the intial language in the context.

opw-681167

note: no need for >=saas-11

openerp/addons/base/ir/ir_qweb.py

@@ -439,9 +439,8 @@ class QWeb(orm.AbstractModel):
         d = qwebcontext.copy()
 
         if 'lang' in template_attributes:
-            init_lang = d.context.get('lang', 'en_US')
             lang = template_attributes['lang']
-            d.context['lang'] = self.eval(lang, d) or lang
+            d.context = dict(d.context, lang=self.eval(lang, d) or lang)
             if not self.pool['res.lang'].search(d.cr, d.uid, [('code', '=', d.context['lang'])], count=True, context=d.context):
                 _logger.info("'%s' is not a valid language code, is an empty field or is not installed, falling back to en_US", lang)
 
@@ -458,10 +457,6 @@ class QWeb(orm.AbstractModel):
         d['generated_attributes'] = generated_attributes
         res = self.render(cr, uid, template, d)
 
-        # we need to reset the lang after the rendering
-        if 'lang' in template_attributes:
-            d.context['lang'] = init_lang
-
         return res
 
     def render_tag_call_assets(self, element, template_attributes, generated_attributes, qwebcontext):