Hello ACC , I added it to Polyglot => Key => "_sys_txt_join_description" . 

This what I ended up using below. This added a button with text, "Log in Here".

<script>
$(document).ready(function(){
$("a[href$='login']").attr("class", "bx-form-input-submit bx-btn bx-btn-primary");});
</script>
<strong><a href="{0}">Log in here</a></strong>