WordPress: Font Library でオリジナルのフォントコレクションを追加する

functions.php

<?php

add_action( 'init', 'themeslug_add_font_collections' );

/**
 * フォントコレクションを追加する
 */
function themeslug_add_font_collections() {

// フォントファミリーの定義:
$font_families = [
  [
    'font_family_settings' => [
      'fontFamily' => 'Open Sans, sans-serif',
      'slug' => 'open-sans',
      'name' => 'Open Sans',
      'fontFace' => [
        [
          'fontFamily' => 'Open Sans',
          'fontStyle' => 'normal',
          'fontWeight' => '300',
          'src' => 'https://fonts.gstatic.com/s/opensans/v40/memSYaGs126MiZpBA-UvWbX2vVnXBbObj2OVZyOOSr4dVJWUgsiH0C4iY1M2xLER.woff2',
        ],
        [
          'fontFamily' => 'Open Sans',
          'fontStyle' => 'italic',
          'fontWeight' => '400',
          'src' => 'https://fonts.gstatic.com/s/opensans/v40/memQYaGs126MiZpBA-UFUIcVXSCEkx2cmqvXlWq8tWZ0Pw86hd0Rk8ZkaVIUwaERZjA.woff2'
        ],
      ],
    ],
    'categories' => [ 'sans-serif' ],
  ],
  [
    'font_family_settings' => [
      'fontFamily' => 'Monoton, system-ui',
      'slug' => 'monoton',
      'name' => 'Monoton',
      'fontFace' => [
        [
        'fontFamily' => 'Monoton',
        'fontStyle' => 'normal',
        'fontWeight' => '400',
        'src' => 'https://fonts.gstatic.com/s/monoton/v19/5h1aiZUrOngCibe4fkPBQ2S7FU8.woff2',
        'preview' => 'https://s.w.org/images/fonts/17.7/previews/monoton/monoton-400-normal.svg'
        ],
      ],
    ],
    'categories' => [ 'display' ],
  ],
  [
    'font_family_settings' => [
      'fontFamily' => 'Arial, Helvetica, Tahoma, Geneva, sans-serif',
      'slug' => 'arial',
      'name' => 'Arial',
    ],
    'categories' => [ 'sans-serif' ],
  ],
];

// フォントカテゴリーの定義:
$categories = [
  [
    'name' => _x( 'Display', 'Font category name' ),
    'slug' => 'display',
  ],
    [
        'name' => _x( 'Sans Serif', 'Font category name' ),
        'slug' => 'sans-serif',
    ],
];

$config = [
    'name' => '私のフォントコレクション',
    'description' => '私が好きなフォントのコレクション。',
    'font_families' => $font_families,
    'categories' => $categories,
];

// フォントコレクション（フォントファミリーとカテゴリー）を登録する:
wp_register_font_collection ( 'my-font-collection', $config );

}

WordPress.org post:

• New Feature: Font Library – Make WordPress Core

Japanese post:

• WordPress のフォント機能（ Font Library ）の使い方 - 実践 WordPress