I've noticed that all language tags are sorted first but clojure tag.
Is this by design or is there some setting that this tag is missing?
There is no special attribute about tags that make them 'language' tags.
Tags are sorted on the number of questions that have that tag, so if some non-language tag has more questions tagged with it, that tag will come first.
Look through the list of questions and you will see how that happens.
It just so happens that most popular languages have far more questions than the other tags that are added, so they sort first. If you have a look at all the tags you will see that questions tagged with performance will have performance tag sorted ahead of most languages other than the most popular.