Javascript errors: Failed while initializing "select2" pattern

I'm getting the following JS errors in my console when I open a news item to edit it. I suspect this explains why I can't add external links.

plone-logged-in-compiled.min.js:1 patterns.pat.select2: Failed while initializing "select2" pattern. TypeError: a.$el.select2 is not a function(…)b.output @ plone-logged-in-compiled.min.js:1
plone-logged-in-compiled.min.js:1 patterns.pat.select2: Failed while initializing "select2" pattern. TypeError: a.$el.select2 is not a function(…)b.output @ plone-logged-in-compiled.min.js:1
plone-logged-in-compiled.min.js:1 patterns.pat.relateditems: Failed while initializing "relateditems" pattern. TypeError: a.$el.select2 is not a function(…)b.output @ plone-logged-in-compiled.min.js:1
plone-logged-in-compiled.min.js:1 patterns.pat.select2: Failed while initializing "select2" pattern. TypeError: a.$el.select2 is not a function(…)b.output @ plone-logged-in-compiled.min.js:1
plone-logged-in-compiled.min.js:1 patterns.pat.select2: Failed while initializing "select2" pattern. TypeError: a.$el.select2 is not a function(…)b.output @ plone-logged-in-compiled.min.js:1
plone-logged-in-compiled.min.js:1 patterns.pat.select2: Failed while initializing "select2" pattern. TypeError: a.$el.select2 is not a function(…)b.output @ plone-logged-in-compiled.min.js:1
plone-logged-in-compiled.min.js:1 patterns.pat.select2: Failed while initializing "select2" pattern. TypeError: a.$el.select2 is not a function(…)b.output @ plone-logged-in-compiled.min.js:1
plone-logged-in-compiled.min.js:1 patterns.pat.relateditems: Failed while initializing "relateditems" pattern. TypeError: a.$el.select2 is not a function(…)b.output @ plone-logged-in-compiled.min.js:1
plone-logged-in-compiled.min.js:1 patterns.pat.select2: Failed while initializing "select2" pattern. TypeError: a.$el.select2 is not a function(…)b.output @ plone-logged-in-compiled.min.js:1
plone-logged-in-compiled.min.js:1 patterns.pat.select2: Failed while initializing "select2" pattern. TypeError: a.$el.select2 is not a function(…)b.output @ plone-logged-in-compiled.min.js:1
http://mysite.com/++plone++static/components/tinymce-builded/js/tinymce/langs/en-gb.js Failed to load resource: the server responded with a status of 404 (Not Found)
http://mysite.com/++plone++static/components/tinymce-builded/js/tinymce/langs/en-gb_EN-GB.js Failed to load resource: the server responded with a status of 404 (Not Found)

I was able to add the link when using the Barceloneta theme so now I'm trying to figure out what's missing from my theme.

Hi pigeonflight,
I have the same your problem, but it doesn't solve using Barceloneta theme.
Did you find where the problem is, so I can find my mistake?
Thanks

I don't recall how I solved this but here are two resources: