Child theme functions.php snippet which enqueues parent theme styles, loads languages from child theme and copies settings from parent theme to child theme.

functions.php

  <?php
  /*
   * Author: Onni Hakala / Seravo Oy
   * Source: https://gist.github.com/onnimonni/8f58e72bc433c54f7b17
   * Description: Use these default options which are good for every typical child theme
   * You can just copy-paste this into child-theme functions.php
   */

  if (!class_exists('ChildThemeOptions')) {
    class ChildThemeOptions {

      /*
       * Parent theme slug
       */
      private static $parent_slug;

      /*
       * Theme slug
       */
      private static $theme_slug;

      // Add our filters for the child theme
      function __construct(){

        /*
         * Enqueue child theme styles
         */
        add_action( 'wp_enqueue_scripts', array(__CLASS__, 'parent_theme_enqueue_styles' ));

        /*
         * Use translations from child theme
         */
        add_action( 'after_setup_theme', array(__CLASS__, 'child_theme_locale' ));

        /*
         * Copy parent theme options during child theme activation
         */
        add_action( 'after_switch_theme', array(__CLASS__, 'setup_options_from_parent_theme'));

        // Set slug variables for later usage
        self::$parent_slug = wp_get_theme()->get('Template');
        self::$theme_slug = basename(get_stylesheet_directory());
      }

      /**
       * Enqueue parent theme styles as well and make styles of this theme dependent on parent
       */
      public static function parent_theme_enqueue_styles() {
          wp_enqueue_style( 'parent-theme-style', get_template_directory_uri() . '/style.css' );
          wp_enqueue_style( 'child-theme-style',
              get_stylesheet_directory_uri() . '/style.css',
              array('parent-theme-style')
          );
      }

      /**
       * Load translations for the parent theme so they are not removed when theme is updated
       */
      public static function child_theme_locale() {
          load_child_theme_textdomain( self::$parent_slug, get_stylesheet_directory() . '/languages' );
      }

      /**
       * Many times users have already equipped the parent theme with correct options
       * When activiting this theme just copy them from parent theme so that 
       * user doesn't have to setup them again.
       * This is only done once.
       */
      public static function setup_options_from_parent_theme() {
        $parent_options = get_option( 'theme_mods_'.self::$parent_slug );
        $options_already_setted = get_option( 'theme_'.self::$theme_slug.'_copied_from_parent', false);
        if ($parent_options and !$options_already_setted) {
          update_option('theme_mods_'.self::$theme_slug,$parent_options);

          // We want this to only happen once so write it in to memory
          update_option('theme_'.self::$theme_slug.'_copied_from_parent',true);
        }
      }

    } // End Class: ChildThemeOptions

    new ChildThemeOptions();
  }