[In warning North Korea, Tillerson said, Trump was merely speaking in language that its leader, Kim Jong Un, "can understand."]
If there is anyone that Trump should not copy or "speak in a language they can understand" it would be Kim Jong-un.  It is exactly that language and actions that have led to North Korea becoming isolated and marginalized to the point that the only thing that the anyone pays attention to is the threat of using hard power.
Trump has already done a great job of alienating our allies.  Every time he opens his mouth his cabinet has to clean up the mess.  I'll bet Tillerson (diplomacy) and Mattis (military) are tired of rationalizing or temporizing Trump's rhetoric without Trump complicating things even more by "copying" the leader of what is arguably the worst nation when it comes to international relations.