Naruto Uzumaki's "dattebayo" ( だってばよ) verbal tic comes in many forms. The early anime dub by Viz Media translated it as "Believe it!" Later on, it was changed to a simple "ya know." The manga didn't even use either of these terms until Naruto met Killer Bee; until then, it is omitted entirely. The problem is that there's no direct English equivalent to dattebayo, so nobody knew how to best convey the catchphrase to American audiences.
The issue becomes more complicated when taking the rest of his family into account. The same "ya know" translation is used for his mother Kushina's "dattebane" (だってばね) and the "dattebasa" (だってばさ) of his son Boruto, but that doesn't seem quite right, either. Finding the proper translation for dattebayo will require a better understanding of the term and how it's used.
To better understand dattebayo, it must be dissected and broken down into its individual parts. The first part of this phrase is the simple"da" (だ). It's used at the end of sentences when describing something or explaining what something is. It's the informal version of "desu" (です). A good way to think about it is as an "it is," just at the end of a sentence rather than in the middle of it. Many agree that this use remained unchanged for dattebayo since both are used to cap off sentences.
The "ttebayo" (ってばよ) is a little more divisive among translators. The "tte" (って) can be paired with either the "da" or the "bayo" (ばよ). If it's the former, then it forms "datte" (だって), a suffix indicative of something that's been said. Ttebayo on the other hand can be used to mean "you know." The translators likely recognized the latter meaning and used it as the default. This can be seen as correct in the sense that it's Naruto trying to get people to understand his point of view.
To get more specific, yo (よ) is used as an absolute statement of fact. It functions in much the same way as an exclamation mark in English. When someone wants to stress how certain they are or how irrefutable what they're saying is, they will often put "yo" at the end of their sentence. It usually follows "da," which is probably what trips up translators; to amateurs, the "tteba" in the middle of Naruto's catchphrase may look like a bunch of unnecessary gibberish, hence the simplification.
If Naruto's dattebayo can be interpreted as him giving his sentences as a statement of fact, then "Believe it!" could work. Naruto had always wanted to prove he has what it takes to become Hokage despite what everyone says about him. In this regard, dattebayo could be his response to all the naysayers in his life.
Another way of looking at Naruto's catchphrase is "I tell ya!" This translation came about when Killer Bee was coming up with new verses for his enka raps. He used "ttebayo," but he was puzzled over the missing piece. It's only when Bee heard Naruto say dattebayo that the lightbulb went off in his head. This translation is loose but passable.
The key takeaway from Naruto's dattebayo is that he's making a statement. Naruto's Nindō or "Ninja Way" is about never going back on his word. To that end, when he says dattebayo, it's a sort of promise that he stands by what he says. The catchphrase cannot be directly translated into English, so whoever's in charge of localization can take creative liberty with it. However, they must get across Naruto's steadfast resolve in order for it to be called a proper translation.