message: force the use of the en_US dictionary
  check_spelling_pedantic uses aspell, which uses the system dictionary
  unless told otherwise. Envoy's codebase has settled on using en_US as
  its dictionary, so we should force aspell to use it as well.
diff: @@ -97,7 +97,9 @@ class SpellChecker:
  f.writelines(words)
  # Start an aspell process.
  - aspell_args = ["aspell", "pipe", "--run-together", "--encoding=utf-8", "--personal=" + pws]
  + aspell_args = [
  + "aspell", "pipe", "--run-together", "--lang=en_US", "--encoding=utf-8", "--personal=" + pws
  + ]
  self.aspell = subprocess.Popen(
  aspell_args,
  bufsize=4096,
  