While a percentage is printed in the console log for the minecraft client, there is no longer a loading bar, starting after 1.2.5. I assume this was a side effect of switching to a server -> local client framework. It should i would assume be easy to implement it by reading percentage from the console.
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Duplicate of MC-2681, please use the search function to see if your bug has already been submitted. Currently over 50% of tickets are being closed as duplicate.
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