getting tweets written in sinhala language and saving in csv file

Question

The below part of code fetches all tweets for a specific user and stores them into a CSV file. when I convert tweets written in sinhala language to CSV, Sinhala language characters are not visible correctly. English characters are correctly visible.

Here is my code,

import tweepy #https://github.com/tweepy/tweepy
import csv

#Twitter API credentials
consumer_key = ""
consumer_secret = ""
access_key = ""
access_secret = ""


def get_all_tweets(screen_name):
    #Twitter only allows access to a users most recent 3240 tweets with this method

    #authorize twitter, initialize tweepy
    auth = tweepy.OAuthHandler(consumer_key, consumer_secret)
    auth.set_access_token(access_key, access_secret)
    api = tweepy.API(auth)



    #initialize a list to hold all the tweepy Tweets
    alltweets = []  

    #make initial request for most recent tweets (200 is the maximum allowed count)
    new_tweets = api.user_timeline(screen_name = screen_name,count=200)

    #save most recent tweets
    alltweets.extend(new_tweets)

    #save the id of the oldest tweet less one
    oldest = alltweets[-1].id - 1

    #keep grabbing tweets until there are no tweets left to grab
    while len(new_tweets) > 0:
        print "getting tweets before %s" % (oldest)

        #all subsiquent requests use the max_id param to prevent duplicates
        new_tweets = api.user_timeline(screen_name = screen_name,count=200,max_id=oldest)

        #save most recent tweets


        alltweets.extend(new_tweets)

        #update the id of the oldest tweet less one
        oldest = alltweets[-1].id - 1

        print "...%s tweets downloaded so far" % (len(alltweets))

    #transform the tweepy tweets into a 2D array that will populate the csv 
    outtweets = [[tweet.id_str, tweet.created_at, tweet.text.encode("utf-8")]for tweet in alltweets]

    #write the csv  
    with open('%s_tweets.csv' % screen_name, 'wb') as f:
        writer = csv.writer(f)
        writer.writerow(["id","created_at","text"])
        writer.writerows(outtweets)

    pass


if __name__ == '__main__':
    #pass in the username of the account you want to download
    get_all_tweets("irajonline")

How can I make Sinhala language tweets correctly visible when converted into CSV format?