Adds a "Translate" button to the admin bar, on post-edit and front end pages, that links directly to the WeGlot visual editor for that page.

admin-bar-for-weglot.php

<?php if(!defined('ABSPATH')) { die(); }

/*
Plugin Name: Admin Bar for WeGlot
Plugin URI: https://gschoppe.com
Description: Adds an admin bar link to translate any page on your site
Version: 0.1.0
Author: Greg Schoppe
Author URI: https://gschoppe.com
Text Domain: weglotadminbar
Domain Path: /languages
*/

if( !class_exists('WeGlot_AdminBarButton') ) {
	class WeGlot_AdminBarButton {
		public static function Instance() {
			static $instance = null;
			if ($instance === null) {
				$instance = new self();
			}
			return $instance;
		}

		private function __construct() {
			add_action( 'wp_before_admin_bar_render', array( $this, 'add_admin_button' ) );
      add_action( 'admin_head', array( $this, 'admin_bar_styles' ) );
      add_action( 'wp_head', array( $this, 'admin_bar_styles' ) );
		}

    public function add_admin_button() {
    	global $wp_admin_bar;
      $url = $this->get_current_page_url();
    	if( $url ) {
    		$wp_admin_bar->add_menu( array(
    			'parent' => false,
    			'id'     => 'weglot_translate',
    			'title'  => __('Translate', 'weglotadminbar'),
    			'href'   => 'http://dashboard.weglot.com/visual-editor/?url=' . urlencode( $url ),
    			'meta'   => array(
    				//'html'      => '',
    				//'class'     => '',
    				//'onclick'   => '',
    				'target'    => '_blank',
    				'title'     => __('Translate with WeGlot', 'weglotadminbar' )
    			)
    		) );
    	}
    }

    public function admin_bar_styles() {
      $weglot_icon = plugins_url() . "/weglot/images/weglot_fav_bw.png";
?>
<style type="text/css">
body.admin-bar #wpadminbar #wp-admin-bar-weglot_translate a:before {
  content: ' ';
  display: inline-block;
  width: 20px;
  height: 20px;
  margin-top: 3px;
  background-image: url('<?php echo $weglot_icon; ?>') !important;
  background-size: contain;
  background-position: center center;
  background-repeat: no-repeat;
}
body.admin-bar #wpadminbar #wp-admin-bar-weglot_translate a:hover:before {
  opacity: 0.6;
}
</style>
<?php
    }

    private function get_current_page_url() {
      if( !is_admin() ) {
        $domain = $this->get_site_domain();
        $url = $domain . $_SERVER['REQUEST_URI'];
        return $url;
      } else {
        if( function_exists( "get_current_screen" ) )
        $screen = get_current_screen();
        if( empty( $screen->base ) || $screen->base != 'post' ) {
          return false;
        }
        $id = get_the_ID();
        $permalink = get_the_permalink( $id );
        if( !$id || !$permalink ) {
          return false;
        }
        return $permalink;
      }
    }

    private function get_site_domain() {
      $url = untrailingslashit( get_site_url() );
      $path = parse_url( $url, PHP_URL_PATH );
      if( $path ) {
        $url = preg_replace('/'. preg_quote($path, '/') . '$/', '', $url);
        $url = untrailingslashit( $url );
      }
      return $url;
    }
	}
	WeGlot_AdminBarButton::Instance();
}