I checked, actually it doesn't let you leave the comment in the translated part, so you have to go back to the original post.

For the button, I use steem-fanbase, just have the Whalevault extension and use the Steemit posting key, after that just click on "add translation button" and a page pops up with your posts that you want to add the button to.

Otherwise you can do it manually by going to google site translator, enter the link of your post and google will create another page of your translated post with another link. You then go back to your original post, click on edit post and enter the link and save the updates.

I hope I've been helpful, if you need further clarification please let me know. 😊