Fix 201302mb

Target Commit: 5fe4843

Description:

We get the content to be broadcast too short due to the multibyte language like d15dd27, the foregoing my commit.

"mb_strlen" and "mb_subsrt" are added along with the check on the existence of the functions.

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P.S.

I would like to add the excerpt as a token and am not sure I should add that modification on this commit.  I've created another branch and commit for it.  Should I merge the pull request or submit another if I want to share?