I'm not able to recreate the issue with the missing 'Next' button in my own Mamut installation, but please upgrade to version 17.2 if you have an older version: http://www.mamut.com/uk/mbs17/
Improvements have been made to this module in the latest versions. Additionally, installing the latest version (or reinstalling the same) will register language constants again.
I assume you have tried to expand/maximize the window.
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