So the primary thing to look at for compatibility is the sizing of the steerer tube. I'm not sure what the Langster is (may depend on the year) I'd guess it's probably 1 1/8 as that's been the most common in the last decade. Other "common" sizes are 1" and tapered (generally 1 1/8 to 1 1/2) so long as you replace the right size, it'll generally fit (langster doesn't have any weird design that would stop it that I know of)
Your rake/trail is also a consideration you should keep in mind, as changing it can have (sometimes drastic) effects on the handling/stability of the bike. For the most part on a track bike going in a circle, you probably won't notice subtle changes ( a mm or two)
Last thing to keep in mind is if you're going from one material steerer tube to another (carbon to alum or vice versa) you may need a different style expander for the headset. Don't beat a star nut into a carbon steerer! Some forks also don't come with the crown race pre-installed, not really an issue to do/have done, but just something to keep in mind.