Right now Reftoolbar is only available on English Wikipedia (although there is a very limited version on Malayalam Wikipedia). It has frequently been requested that it be turned into an extension so that other Wikipedias can also use it.

This card tracks a proposal from the 2015 Community Wishlist Survey: https://meta.wikimedia.org/wiki/2015_Community_Wishlist_Survey

This proposal received 23 support votes, and was ranked #40 out of 107 proposals. https://meta.wikimedia.org/wiki/2015_Community_Wishlist_Survey/Editing#Turn_RefToolbar_into_a_MediaWiki_extension_.28or_add_it_into_the_WikiEditor_extension.29

Note: Ed Sanders wrote:
We already have Citoid, which does a great job of inserting references automatically (from a URL) or manually (pretty much the same as RefToolbar). This would a duplication of that work. If you opt in to VE you can still use the wikitext editor for all your editing, and just switch to VisualEditor (mid-edit if necessary) if you want to add a citation. If you opt out of new features you don't get new features...