Twisted Internationalization
I haven't worked with Twisted, 
and also cannot recommend existing internationalization implementations,
but I can code review in terms of Python in general.

You are not following PEP8,
the official coding style guide of Python.
The coding style violations are not so bad but they are noticeable.
I won't comment on those one by one,
I suggest to give the doc a good read and follow it.

It's nice that you documented this method with a comment:


## load the JSON resource from the path and return the parse obj (dict in this case)
def getJSON(path):
  file = open(path)
  data = json.load(file)
  file.close()
  return data



Why not go all the way and document with a proper docstring?
Also, closing files manually is old-fashioned. 
The recommend way is simpler and better:

def getJSON(path):
    """
    load the JSON resource from the path and return the parse obj (dict in this case)

    @param path: JSON file to parse
    @return: parsed object as a dict
    """
    with open(path) as fh:
        return json.load(fh)


In this code, the initialization of locales = [] is unnecessary,
because you assign to the variable in both branches of the if, so you can remove it:


    locales = []
    if setLocales:
      locales = json.load(setLocales)
    else:
      lang_header = request.headers.get("Accept-Language", "en") # for example en-US,en;q=0.8,es;q=0.6
      locales = [locale.split(';')[0] for locale in lang_header.split(',')]