Add a language field

[dfabulich]

iftechfoundation/ifdb#1345

Right now, you can leave the language field blank. Not that many games do, only 778 out of the ~15K games in our DB.

But we could make it mandatory, instead.

If we did this, in order for my automated IFComp importer to work, I'd need to have an automated way of knowing what language(s) a game was published in. Specifically, I'd need to be able to compute a <language> element, as defined by the Treaty of Babel.

iftechfoundation/ifdb#1346

https://babel.ifarchive.org/babel.html#language

The <language> tag is optional, and records the language in which the
work's text is written (or primarily written, if the work uses multiple
languages). This information can help potential users identify works
written in languages they know, and could also be used as a hint to
text-to-speech converters or other natural language analysis tools.

The value is required to be an ISO-639 two- or three-letter language
code, optionally followed by a hyphen and an ISO-3166 country code.
(For English, typical specifiers would be en-US, for US English, or
en-GB, for British English.)

Guidelines:

• Design systems may assume that the language is English, but should
  provide the author with the opportunity to change this if it isn't.
• Where the author has not specified any dialect, none should be
  given: thus the default should be "en", not "en-US" or "en-UK".

We'd need to add a language field to the IFComp DB schema, add it to the author form, display it on the ballot page (and tag it with inLanguage VideoGame schema) https://schema.org/VideoGame and preferably also add it to IFComp's JSON API.