Update: Windows Insider chief Dona Sarkar has taken to Twitter to note that Microsoft is looking into 14998's early release, noting that you "don't need" to install the update.
Original story: So here's an interesting thing, if you're an Insider using Windows 10 Mobile on the Fast Ring, checking for updates might land you with a peculiar update tagged "Localization for English". Before you write this off as something super boring, take note of how long the update takes to download. Turns out, this update is actually build 14998... IN DISGUISE!
We're assuming this build has been accidently pushed out to Insiders, considering Microsoft hasn't made an official announcement about it. The update being incorrectly tagged in Windows Update likely means Microsoft did not intend for this update to go out just yet, or at all.
So with that in mind, if you're not willing to take any risks, don't check for updates right now, not until we get confirmation from Microsoft that this build is something they want Insiders messing with. In fact, we're going to advise against installing this build for now. Even if the upgrade does work (which it did for us on a Lumia 950 XL), there's no guaranteeing you'll be able to install the next build if this build wasn't supposed to be released.
If you can't see the update tagged "Localization for English", then Microsoft may have already pulled it by the time you see this article. Stay tuned at Windows Central for more regarding this surprise new build, including what's new, improved and more!
Thanks for the tips, everyone!