I use Mastodon Autopost (github.com/simonfrey/mastodon_wordpress_autopost) for this. (I think originally came across it via Chris Aldrich). You can choose per post whether you want to post to your instance. I also added a couple of very hacky functions (github.com/ngm/semloop/blob/master/includes/syndication-targets.php) to add it as a Micropub syndication target.
Woop woop! Hacked together a target to syndicate posts to my Mastodon instance when posting via Micropub.
One thing I’m really enjoying about Mastodon is the plurality of languages. I don’t know if it’s random or by design, or simply a product of my network, but I see toots in various languages, and I find this very healthy.