[fix] bing paging and language support

see https://msdn.microsoft.com/en-us/library/ff795620.aspx for bing
specific search operators

closes #755

searx/engines/bing.py

@@ -32,18 +32,13 @@ search_string = 'search?{query}&first={offset}'
 def request(query, params):
     offset = (params['pageno'] - 1) * 10 + 1
 
-    if params['language'] == 'all':
-        language = 'en-US'
-    else:
-        language = params['language'].replace('_', '-')
+    if params['language'] != 'all':
+        query = 'language:{} {}'.format(params['language'].split('_')[0].upper(), query)
 
     search_path = search_string.format(
-        query=urlencode({'q': query, 'setmkt': language}),
+        query=urlencode({'q': query}),
         offset=offset)
 
-    params['cookies']['SRCHHPGUSR'] = \
-        'NEWWND=0&NRSLT=-1&SRCHLANG=' + language.split('-')[0]
-
     params['url'] = base_url + search_path
     return params
 

tests/unit/engines/test_bing.py

@@ -14,14 +14,12 @@ class TestBingEngine(SearxTestCase):
         params = bing.request(query, dicto)
         self.assertTrue('url' in params)
         self.assertTrue(query in params['url'])
+        self.assertTrue('language%3AFR' in params['url'])
         self.assertTrue('bing.com' in params['url'])
-        self.assertTrue('SRCHHPGUSR' in params['cookies'])
-        self.assertTrue('fr' in params['cookies']['SRCHHPGUSR'])
 
         dicto['language'] = 'all'
         params = bing.request(query, dicto)
-        self.assertTrue('SRCHHPGUSR' in params['cookies'])
-        self.assertTrue('en' in params['cookies']['SRCHHPGUSR'])
+        self.assertTrue('language' not in params['url'])
 
     def test_response(self):
         self.assertRaises(AttributeError, bing.response, None)