function allow(language, only, ignore) {
  if (only.length === 0 && ignore.length === 0) {
    return true
  }

  return (
    (only.length === 0 || only.includes(language)) && !ignore.includes(language)
  )
}
Check if `language` can match according to settings.

@param {string} language
  Languages to filter
@param {Array<string>} only
  Allowed languages; if non-empty, only included languages are kept.
@param {Array<string>} ignore
  Disallowed languages; included languages are ignored.
@return {boolean}
  Whether `language` can match