I believe the repeating kanji indicates that Kaioshin is talking about more than world. Context being that he's moving from one world (or area, realm, boundary, etc) to another. Wiki says "world to world" but what do the native Japanese speakers think
Meaning:keeper of the keys; earth. Kai is a gender-neutral name of Welsh origin, with roots worldwide, including in Greece, Hawaii, Japan, and Scandinavian countries. In Hawaii, Kai means "the sea," while in New Zealand, Kai is the Māori word for "food.
What's this about "separate" and "between X"? The kanji 界 (Kai) literally means "world". Putting it twice as 界界 (Kaikai) emphasizes that meaning; it could translate as "world-world" or "worlds". In the context of a teleportation skill that lets you travel all over the universe, it could be interpreted as moving from one world to another.
But the technique's name is spelled only in katakana as カイカイ (Kaikai), so it's mostly just wordplay, although "moving worlds" is probably still the intent of the pun.
I'm not a native speaker. The existing translations is probably fine. If you wanted to Americanize it you could call it the world jump or dimension teleport.