Applying Changes To WordPress Child functions.php

I need to change various words on the checkout page using Avada and Woocomerce. I want to change them using the child themes function.php. I found where the words are located in various .php files such as review-order.php.

So say I wanted to change the word ‘Subtotal’ to ‘小計’. I can change it easily in the review-order.php but I want to do it in the child function.php so it remains when I update. I can’t figure out how to hook it etc

The code for review-order.php is below, how would I code in the child function.php in order to change this word? If I can see how to do it once, I can do it again for all the other words.

<?php
/**
 * Review order table
 *
 * @author      WooThemes
 * @package     WooCommerce/Templates
 * @version     2.3.0
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit;
}
?>
<table class="shop_table woocommerce-checkout-review-order-table">
    <thead>
    <tr>
        <th class="product-name"><?php _e( 'Product', 'woocommerce' ); ?></th>
        <th class="product-total"><?php _e( 'Total', 'woocommerce' ); ?></th>
    </tr>
    </thead>
    <tbody>
    <?php
        do_action( 'woocommerce_review_order_before_cart_contents' );

        foreach ( WC()->cart->get_cart() as $cart_item_key => $cart_item ) {
            $_product     = apply_filters( 'woocommerce_cart_item_product', $cart_item['data'], $cart_item, $cart_item_key );

            if ( $_product && $_product->exists() && $cart_item['quantity'] > 0 && apply_filters( 'woocommerce_checkout_cart_item_visible', true, $cart_item, $cart_item_key ) ) {
                ?>
                <tr class="<?php echo esc_attr( apply_filters( 'woocommerce_cart_item_class', 'cart_item', $cart_item, $cart_item_key ) ); ?>">
                    <td class="product-name">

                        <?php // Avada edit ?>
                        <span class="product-thumbnail">
                                    <?php
                                        $thumbnail = apply_filters( 'woocommerce_cart_item_thumbnail', $_product->get_image(), $cart_item, $cart_item_key );

                                        if ( ! $_product->is_visible() )
                                            echo $thumbnail;
                                        else
                                            printf( '<a href="%s">%s</a>', $_product->get_permalink(), $thumbnail );
                                    ?>
                                </span>
                        <div class="product-info">
                            <?php // Avada edit ?>
                            <?php echo apply_filters( 'woocommerce_cart_item_name', $_product->get_title(), $cart_item, $cart_item_key ); ?>
                            <?php echo apply_filters( 'woocommerce_checkout_cart_item_quantity', ' <strong class="product-quantity">' . sprintf( '&times; %s', $cart_item['quantity'] ) . '</strong>', $cart_item, $cart_item_key ); ?>
                            <?php echo WC()->cart->get_item_data( $cart_item ); ?>

                        </div>
                    </td>
                    <!--<td class="product-name">-->
                    <!--    --><?php //echo apply_filters( 'woocommerce_cart_item_name', $_product->get_title(), $cart_item, $cart_item_key ); ?>
                    <!--    --><?php //echo apply_filters( 'woocommerce_checkout_cart_item_quantity', ' <strong class="product-quantity">' . sprintf( '&times; %s', $cart_item['quantity'] ) . '</strong>', $cart_item, $cart_item_key ); ?>
                    <!--    --><?php //echo WC()->cart->get_item_data( $cart_item ); ?>
                    <!--</td>-->
                    <td class="product-total">
                        <?php echo apply_filters( 'woocommerce_cart_item_subtotal', WC()->cart->get_product_subtotal( $_product, $cart_item['quantity'] ), $cart_item, $cart_item_key ); ?>
                    </td>
                </tr>
            <?php
            }
        }

        do_action( 'woocommerce_review_order_after_cart_contents' );
    ?>
    </tbody>
    <tfoot>

    <tr class="cart-subtotal">
        <th><?php _e( 'Subtotal', 'woocommerce' ); ?></th>
        <td><?php wc_cart_totals_subtotal_html(); ?></td>
    </tr>

    <?php foreach ( WC()->cart->get_coupons() as $code => $coupon ) : ?>
        <tr class="cart-discount coupon-<?php echo esc_attr( $code ); ?>">
            <th><?php wc_cart_totals_coupon_label( $coupon ); ?></th>
            <td><?php wc_cart_totals_coupon_html( $coupon ); ?></td>
        </tr>
    <?php endforeach; ?>

    <?php if ( WC()->cart->needs_shipping() && WC()->cart->show_shipping() ) : ?>

        <?php do_action( 'woocommerce_review_order_before_shipping' ); ?>

        <?php wc_cart_totals_shipping_html(); ?>

        <?php do_action( 'woocommerce_review_order_after_shipping' ); ?>

    <?php endif; ?>

    <?php foreach ( WC()->cart->get_fees() as $fee ) : ?>
        <tr class="fee">
            <th><?php echo esc_html( $fee->name ); ?></th>
            <td><?php wc_cart_totals_fee_html( $fee ); ?></td>
        </tr>
    <?php endforeach; ?>

    <?php if ( WC()->cart->tax_display_cart === 'excl' ) : ?>
        <?php if ( get_option( 'woocommerce_tax_total_display' ) === 'itemized' ) : ?>
            <?php foreach ( WC()->cart->get_tax_totals() as $code => $tax ) : ?>
                <tr class="tax-rate tax-rate-<?php echo sanitize_title( $code ); ?>">
                    <th><?php echo esc_html( $tax->label ); ?></th>
                    <td><?php echo wp_kses_post( $tax->formatted_amount ); ?></td>
                </tr>
            <?php endforeach; ?>
        <?php else : ?>
            <tr class="tax-total">
                <th><?php echo esc_html( WC()->countries->tax_or_vat() ); ?></th>
                <td><?php echo wc_price( WC()->cart->get_taxes_total() ); ?></td>
            </tr>
        <?php endif; ?>
    <?php endif; ?>

    <?php do_action( 'woocommerce_review_order_before_order_total' ); ?>

    <tr class="order-total">
        <th><?php _e( 'Total', 'woocommerce' ); ?></th>
        <td><?php wc_cart_totals_order_total_html(); ?></td>
    </tr>

    <?php do_action( 'woocommerce_review_order_after_order_total' ); ?>

    </tfoot>
</table>

Currently the child functions.php looks like this:

<?php

function theme_enqueue_styles() {
    wp_enqueue_style( 'avada-parent-stylesheet', get_template_directory_uri() . '/style.css' );
}
add_action( 'wp_enqueue_scripts', 'theme_enqueue_styles' );

function avada_lang_setup() {
    $lang = get_stylesheet_directory() . '/languages';
    load_child_theme_textdomain( 'Avada', $lang );
}
add_action( 'after_setup_theme', 'avada_lang_setup' );

<?php

Thanks for your help everyone!