StackOverflow WordPress User Profile Dynamic Child Taxonomy Dropdown Example

functions.php

function slcustom_user_profile_fields( $user ){

	$categories = smyles_get_taxonomy_hierarchy( 'project_category' );
	$parent_category = $user->parent_category;
	$child_category = $user->child_category;
  //	$parent_category = 52; // used for testing
  //	$child_category = 82; // used for testing
	$parent_has_children = ! empty( $parent_category ) && $categories[ $parent_category ] && ! empty( $categories[ $parent_category ]->children );

	// Creative way to use wp_localize_script which creates a JS variable from array
	// You should actually change this to load your JavaScript file and move JS below to that file
	wp_register_script( 'slcustom_user_profile_fields', '' );
	wp_localize_script( 'slcustom_user_profile_fields', 'slcustom_categories', $categories );
	wp_enqueue_script( 'slcustom_user_profile_fields' );
	?>
	<script>
		jQuery( function($){
			// slcustom_categories var should be available here
			$('#parent_category').change( function(e){
				var child_cat_select = $( '#child_category' );
				var term_id = $(this).val();

				console.log( 'Parent Category Changed', term_id );

				// Remove any existing
				child_cat_select.find( 'option' ).remove();
				
				// Loop through children and add to children dropdown
				if( slcustom_categories && slcustom_categories[ term_id ] && slcustom_categories[ term_id ]['children'] ){
					$.each( slcustom_categories[term_id]['children'], function( i, v ){
						child_cat_select.append( '<option value="' + v['term_id'] + '">' + v[ 'name' ] + '</option>');
					});

					// Show if child cats
					$( '#child_category_row' ).show();
				} else {
					// Hide if no child cats
					$( '#child_category_row' ).hide();
				}
			});
			
			// Trigger change on initial page load to load child categories
			$('#parent_category').change();
		});
	</script>
	<h1 id="temppp">Select a parent taxonomy</h1>
	<table class="form-table">
		<tbody>
			<tr>
				<th>
					Parent
				</th>
				<td>
					<select name="parent_category" id="parent_category">
					<?php
						foreach( (array) $categories as $term_id => $cat ){
							?>
							<option value="<?php echo esc_attr( $term_id ) ?>"<?php echo selected( $parent_category, $term_id ); ?>><?php echo $cat->name; ?></option>
							<?php
						}
					?>
					</select>
				</td>
			</tr>
			<tr id="child_category_row" style="<?php if( ! $parent_has_children ){ echo 'display: none;'; }?>">
				<th>
					Child
				</th>
				<td>
					<select name="child_category" id="child_category">
						<?php
							if( $parent_has_children ){
								foreach( (array) $categories[$parent_category]->children as $c_term_id => $child ){
									?>
									<option value="<?php echo esc_attr( $c_term_id ) ?>"<?php echo selected( $child_category, $c_term_id ); ?>><?php echo $child->name; ?></option>
									<?php
								}
							}
						?>
					</select>
				</td>
			</tr>
		</tbody>
	</table>
	<?php
}

add_action( 'show_user_profile', 'slcustom_user_profile_fields' );
add_action( 'edit_user_profile', 'slcustom_user_profile_fields' );

if ( ! function_exists( 'smyles_get_taxonomy_hierarchy' ) ) {
	/**
	 * Recursively get taxonomy and its children
	 *
	 * @param string $taxonomy
	 * @param int    $parent Parent term ID (0 for top level)
	 * @param array  $args   Array of arguments to pass to get_terms (to override default)
	 *
	 * @return array
	 */
	function smyles_get_taxonomy_hierarchy( $taxonomy, $parent = 0, $args = array( 'hide_empty' => false ) ) {

		$defaults = array(
			'parent'     => $parent,
			'hide_empty' => false
		);
		$r        = wp_parse_args( $args, $defaults );
		// get all direct decendants of the $parent
		$terms = get_terms( $taxonomy, $r );
		// prepare a new array.  these are the children of $parent
		// we'll ultimately copy all the $terms into this new array, but only after they
		// find their own children
		$children = array();
		// go through all the direct decendants of $parent, and gather their children
		foreach ( $terms as $term ) {
			// recurse to get the direct decendants of "this" term
			$term->children = smyles_get_taxonomy_hierarchy( $taxonomy, $term->term_id );
			// add the term to our new array
			$children[ $term->term_id ] = $term;
		}

		// send the results back to the caller
		return $children;
	}
}

Hello,
I want to need multiple child category dropdwon like Parent=>child=>subchild
if possible in this above code
thanks.

Example: Country, State, City