Workshops: Change the Language field to a single-select with locales as options

[coreymckrill]

Instead of an open text field, which is prone to typos and other user errors, the language field would work much better as a select element with a list of locales, where the label of each option is the name of the locale (e.g. Spanish (Mexico) ) and the option value is the ISO code (e.g. es_MX). Ideally the select would have functionality like Select2, where you can begin typing to search and narrow down the list of available choices.

[coreymckrill]

Fixed by #107