Link field with Linkit enabled does not validate with clientside validation and creates wrong link

Hey Drupalistas

Not sure if my title is clear enough.

I have a link field with the linkit plugin enabled to it.
--> "Enable Linkit for this field." on the link field.

This is working as seen in the screenshots. [1, 2, 3]
As you also can see, the output is also something correct: /sites/default/files/user_uploads/86050709581.pdf

When I save the field, it gives me the following error.
"Please fill in a valid URL". [4, 5]
NOTE: It does work when I just select a node in the linkit field... "node/12".

Now, if I disable the clientside validation, it will save the node but the output is
http://testsite.dev/nl//sites/default/files/user_uploads/86050709581.pdf

And that url will not work so I had to create a .htaccess rewrite ...

Is there a way that /sites/xxx will remove the language parameter so it would be a correct link?