You can find all the available services supported by AddThis in the following pages.
AddThis – Service Codes
For example, if you want to add the Reddit button, check the code in the above link. The code is reddit. So you need to append addthis_button_ to the reddit and set it as the class. Finally, add the following line to your AddThis code snippets.
AddThis is great tool for bringing the benefits of social networks to your website. By default the Facebook Like Button provided by AddThis will be translated into different language based on the browser user agent. But you can enforce it to English by adding the the fb:like:locale attribute to the code as follow.
<a class="addthis_button_facebook_like" fb:like:layout="button_count" fb:like:locale="en_US"></a>
Reference: AddThis forum – Default “Facebook Like” button language