fix twitter engine and add comments

* add language-support
* add comments
* little refactoring

searx/engines/twitter.py

+## Twitter (Social media)
+# 
+# @website     https://www.bing.com/news
+# @provide-api yes (https://dev.twitter.com/docs/using-search)
+# 
+# @using-api   no
+# @results     HTML (using search portal)
+# @stable      no (HTML can change)
+# @parse       url, title, content
+#
+# @todo        publishedDate
+
 from urlparse import urljoin
 from urllib import urlencode
 from lxml import html
 from cgi import escape
 
+# engine dependent config
 categories = ['social media']
+language_support = True
 
+# search-url
 base_url = 'https://twitter.com/'
 search_url = base_url+'search?'
+
+# specific xpath variables
+results_xpath = '//li[@data-item-type="tweet"]'
+link_xpath = './/small[@class="time"]//a'
 title_xpath = './/span[@class="username js-action-profile-name"]//text()'
 content_xpath = './/p[@class="js-tweet-text tweet-text"]//text()'
 
 
+# do search-request
 def request(query, params):
     params['url'] = search_url + urlencode({'q': query})
+
+    # set language if specified
+    if params['language'] != 'all':
+        params['cookies']['lang'] = params['language'].split('_')[0]
+
     return params
 
 
+# get response from search-request
 def response(resp):
     results = []
+
     dom = html.fromstring(resp.text)
-    for tweet in dom.xpath('//li[@data-item-type="tweet"]'):
-        link = tweet.xpath('.//small[@class="time"]//a')[0]
+
+    # parse results
+    for tweet in dom.xpath(results_xpath):
+        link = tweet.xpath(link_xpath)[0]
         url = urljoin(base_url, link.attrib.get('href'))
         title = ''.join(tweet.xpath(title_xpath))
         content = escape(''.join(tweet.xpath(content_xpath)))
+
+        # append result
         results.append({'url': url,
                         'title': title,
                         'content': content})
+
+    # return results
     return results