old_contents: import { currentStoreView } from '@vue-storefront/core/lib/multistore'
  import dayjs from 'dayjs'
  import dayjsLocalizedFormat from 'dayjs/plugin/localizedFormat'
  import { once } from '../helpers';
  
  once('__VUE_EXTEND_DAYJS_LOCALIZED_FORMAT__', () => {
    dayjs.extend(dayjsLocalizedFormat)
  })
  
  /**
   * Converts date to format provided as an argument or defined in config file (if argument not provided)
   * @param {String} date
   * @param {String} format
   */
  export function date (date, format) {
    const displayFormat = format || currentStoreView().i18n.dateFormat
    let storeLocale = currentStoreView().i18n.defaultLocale.toLocaleLowerCase()
    const separatorIndex = storeLocale.indexOf('-')
    const languageCode = separatorIndex ? storeLocale.substr(0, separatorIndex) : storeLocale
  
    const isStoreLocale = dayjs().locale(storeLocale).locale()
    const isLanguageLocale = dayjs().locale(languageCode).locale()
    const locale = isStoreLocale || isLanguageLocale
  
    if (locale) return dayjs(date).locale(languageCode).format(displayFormat)
    return dayjs(date).format(displayFormat)
  }
  
new_contents: import { currentStoreView } from '@vue-storefront/core/lib/multistore'
  import dayjs from 'dayjs'
  import dayjsLocalizedFormat from 'dayjs/plugin/localizedFormat'
  import { once } from '../helpers';
  
  once('__VUE_EXTEND_DAYJS_LOCALIZED_FORMAT__', () => {
    dayjs.extend(dayjsLocalizedFormat)
  })
  
  /**
   * Converts date to format provided as an argument or defined in config file (if argument not provided)
   * @param {String} date
   * @param {String} format
   */
  export function date (date, format) {
    const displayFormat = format || currentStoreView().i18n.dateFormat
    let storeLocale = currentStoreView().i18n.defaultLocale.toLocaleLowerCase()
    const separatorIndex = storeLocale.indexOf('-')
    const languageCode = (separatorIndex > -1) ? storeLocale.substr(0, separatorIndex) : storeLocale
  
    const isStoreLocale = dayjs().locale(storeLocale).locale()
    const isLanguageLocale = dayjs().locale(languageCode).locale()
    const locale = isStoreLocale || isLanguageLocale
  
    if (locale) return dayjs(date).locale(languageCode).format(displayFormat)
    return dayjs(date).format(displayFormat)
  }
  
subject: Check separatorIndex is > -1 instead of truthiness