Mac - The vanilla launcher keeps crashing

There could be a few reasons your launcher might be crashing, if the steps in Nothing happens when I click on "Play" what can I do? don't help, then you may be able to work around the problem by force setting the locale when you launch the vanilla launcher. If you are affected by this issue you may see an entry in the log that reads something like this:

terminating with uncaught exception of type std::runtime_error: collate_byname<char>::collate_byname failed to construct for  

To work around this issue, open terminal and enter the following command:

LC_ALL=en_US.UTF-8 /Applications/