This can be easily achieve by using the Twitter's newly added feature Tweet Button!

Here is how you can make your longest tweet.

Just type this URI on your address bar http://twitter.com/share?text=&url=yourtext

Change yourtext to whatever you want (make it more lengthy and use whatever language you want) and bang! The longest tweet created! It's working simply because of the validation error in the url shortening of t.co, I reckon! Hope this might be fixed very soon. But, until then you can make longest tweets after all! Happy tweeting.. oh. happy looongest tweeting!!