function normalizeOption(blockName, option) {
  /** @type {Set<string>} */
  let lang

  if (Array.isArray(option.lang)) {
    lang = new Set(option.lang)
  } else if (typeof option.lang === 'string') {
    lang = new Set([option.lang])
  } else {
    lang = new Set()
  }

  let hasDefault = false
  for (const def of DEFAULT_LANGUAGES[blockName] || []) {
    if (lang.has(def)) {
      lang.delete(def)
      hasDefault = true
    }
  }
  if (lang.size === 0) {
    return {
      lang,
      allowNoLang: true
    }
  }
  return {
    lang,
    allowNoLang: hasDefault || Boolean(option.allowNoLang)
  }
}
Normalizes a given option.
@param {string} blockName The block name.
@param {UserBlockOptions} option An option to parse.
@returns {BlockOptions} Normalized option.