"1 item in cart" is display form Below file.

vendor/magento/module-checkout/view/frontend/web/template/summary/cart-items.html

<div class="title" data-role="title">
    <strong role="heading"><span data-bind="text: getItemsQty()"></span>
        <!-- ko if: getItemsQty() == 1 -->
        <!-- ko i18n: 'Item in Cart' --><!-- /ko -->
        <!-- /ko -->
        <!-- ko if: getItemsQty() > 1 -->
        <!-- ko i18n: 'Items in Cart' --><!-- /ko -->
        <!-- /ko -->
    </strong>
</div>

For translation You need to create module follow below step.

"1 item in cart" is display form Below file. vendor/magento/module-checkout/view/frontend/web/template/summary/cart-items.html

<div class="title" data-role="title">
<strong role="heading"><span data-bind="text: getItemsQty()"></span>
    <!-- ko if: getItemsQty() == 1 -->
    <!-- ko i18n: 'Item in Cart' --><!-- /ko -->
    <!-- /ko -->
    <!-- ko if: getItemsQty() > 1 -->
    <!-- ko i18n: 'Items in Cart' --><!-- /ko -->
    <!-- /ko -->
</strong>

For translation text Item in Cart You need to create module follow below step.

Step-1 create foldar app/i18n/OnTap/en_GB/

step-2 create composer.json file

app/i18n/OnTap/en_GB/composer.json

{
  "name": "ontap/language-en_gb",
  "description": "English (GB) language",
  "version": "1.0.0",
  "license": [
    "OSL-3.0",
    "AFL-3.0"
  ],
  "require": {
    "magento/framework": "100.1.*"
  },
  "type": "magento2-language",
  "autoload": {
    "files": [
      "registration.php"
    ]
  }
}

Step-3 create app/i18n/OnTap/en_GB/language.xml

<?xml version="1.0"?> "urn:magento:framework:App/Language/package.xsd"> <code>en_GB</code> <vendor>OnTap</vendor> <package>en_GB</package> </language>

step-4 create app/i18n/OnTap/en_GB/registration.php

<?php \Magento\Framework\Component\ComponentRegistrar::register( \Magento\Framework\Component\ComponentRegistrar::LANGUAGE, 'ontap_en_gb', __DIR__ );

step-5 create csv file app/i18n/OnTap/en_GB/en_GB.csv add below text

Item in Cart,Item in Basket

remove static data from pub/static/

rm -rf pub/static/frontend

remove cache

rm -rf var/cache/ var/generation/ var/page_cache/ var/view_preprocessed/

genrate static data

php bin/magento setup:static-content:deploy

Now Item in Cart is display with Item in Basket

"1 item in cart" is display form Below file. vendor/magento/module-checkout/view/frontend/web/template/summary/cart-items.html

"1 item in cart" is display form Below file.

vendor/magento/module-checkout/view/frontend/web/template/summary/cart-items.html

<div class="title" data-role="title">
    <strong role="heading"><span data-bind="text: getItemsQty()"></span>
        <!-- ko if: getItemsQty() == 1 -->
        <!-- ko i18n: 'Item in Cart' --><!-- /ko -->
        <!-- /ko -->
        <!-- ko if: getItemsQty() > 1 -->
        <!-- ko i18n: 'Items in Cart' --><!-- /ko -->
        <!-- /ko -->
    </strong>
</div>

For translation You need to create module follow below step.