Do not rely on locale from context as fallback format for date

Since 6c5f4d760e54, the locale key is removed from the RPC context so the
fallback for the date format must come from the translation utilities.

Closes #13290

sao/src/common.js

@@ -228,16 +228,8 @@
     ];
 
     Sao.common.date_format = function(format) {
-        if (jQuery.isEmptyObject(format)) {
-            format = '%x';
-            if (Sao.Session.current_session) {
-                var context = Sao.Session.current_session.context;
-                if (context.locale && context.locale.date) {
-                    format = context.locale.date;
-                }
-            }
-        }
-        return Sao.common.moment_format(format);
+        return Sao.common.moment_format(
+            format || Sao.i18n.locale.date || '%x');
     };
 
     Sao.common.format_time = function(format, date) {

tryton/tryton/common/common.py

@@ -37,6 +37,7 @@ from string import Template
 from threading import Lock, Thread
 
 import tryton.rpc as rpc
+import tryton.translate as translate
 from tryton.cache import CacheDict
 from tryton.config import CONFIG, PIXMAPS_DIR, SOUNDS_DIR, TRYTON_ICON
 
@@ -1528,7 +1529,7 @@ def get_align(float_, expand=True):
 
 
 def date_format(format_=None):
-    return format_ or rpc.CONTEXT.get('locale', {}).get('date', '%x')
+    return format_ or translate.DATE or '%x'
 
 
 def idle_add(func):

tryton/tryton/translate.py

@@ -12,6 +12,7 @@ from gi.repository import Gtk
 from tryton.config import CURRENT_DIR
 
 _ = gettext.gettext
+DATE = None
 
 _LOCALE2WIN32 = {
     'af_ZA': 'Afrikaans_South Africa',
@@ -196,8 +197,10 @@ def setlang(lang=None, locale_dict=None):
         conv = locale.localeconv()
         for field in list(locale_dict.keys()):
             if field == 'date':
-                continue
-            conv[field] = locale_dict[field]
+                global DATE
+                DATE = locale_dict[field]
+            else:
+                conv[field] = locale_dict[field]
         locale.localeconv = lambda: conv