Source

File: wp-admin/includes/class-wp-themes-list-table.php

public function no_items() {
		if ( $this->search_terms || $this->features ) {
			_e( 'No items found.' );
			return;
		}

		$blog_id = get_current_blog_id();
		if ( is_multisite() ) {
			if ( current_user_can( 'install_themes' ) && current_user_can( 'manage_network_themes' ) ) {
				printf(
					/* translators: 1: URL to Themes tab on Edit Site screen, 2: URL to Add Themes screen. */
					__( 'You only have one theme enabled for this site right now. Visit the Network Admin to <a href="%1$s">enable</a> or <a href="%2$s">install</a> more themes.' ),
					network_admin_url( 'site-themes.php?id=' . $blog_id ),
					network_admin_url( 'theme-install.php' )
				);

				return;
			} elseif ( current_user_can( 'manage_network_themes' ) ) {
				printf(
					/* translators: %s: URL to Themes tab on Edit Site screen. */
					__( 'You only have one theme enabled for this site right now. Visit the Network Admin to <a href="%s">enable</a> more themes.' ),
					network_admin_url( 'site-themes.php?id=' . $blog_id )
				);

				return;
			}
			// Else, fallthrough. install_themes doesn't help if you can't enable it.
		} else {
			if ( current_user_can( 'install_themes' ) ) {
				printf(
					/* translators: %s: URL to Add Themes screen. */
					__( 'You only have one theme installed right now. Live a little! You can choose from over 1,000 free themes in the WordPress Theme Directory at any time: just click on the <a href="%s">Install Themes</a> tab above.' ),
					admin_url( 'theme-install.php' )
				);

				return;
			}
		}
		// Fallthrough.
		printf(
			/* translators: %s: Network title. */
			__( 'Only the current theme is available to you. Contact the %s administrator for information about accessing additional themes.' ),
			get_site_option( 'site_name' )
		);
	}