Now that someone else has posted… I shall now provide my new crazy head-canon on how the majority of Ponies are named in universe.
Forgive me if I mangle logic at any point, or ever state the obvious.
Basically, there are several conventions for naming, and it’s possible some of them are regional. And it’s possible that they embody the cultural ideas each ponies family has on what part of their identity is most important as a first impression. Or perhaps how each culture expects to identify others by only a name.
Convention One: Physical Descriptive.
In this convention, the first part of their name is meant to be descriptive of what they look like, or some other quick observation. Twilight (Sparkle) looks like the sky as Night descends, Rainbow (Dash) is Rainbow Colored, Pinkie (Pie) is pink. In theory, this is possibly because that part of their appearance is atypical of their region or background and they live in a society where first social introduction is through word of mouth or written form and being able to tell what someone may look like from a name is an advantage when introducing one’s self; Either so they can pick out who they are looking for in a crowd, or as a way of surprising them by guessing their name before they introduce themselves which would allow one to show that the other has gained a reputation, which may be flattering. One Specific Instance of this last point is when Twilight guessed Rainbow Dash’s name from merely her looks and her actions (see next). Which provoked a response of “The one and only! Why? Have you heard of Me?”. Seems to be often be used in conjunction with Action based names. It’s fairly easy to imagine how the parents choose these names.
Convention Two: Actions
Using a verb in place of part of a name seems to be common enough: Flutter(Shy), (Rainbow) Dash, (Twilight) Sparkle. The main Cultural associations here are that one expects to be able to tell who another pony is by what they will most likely be doing. As with the previous naming convention, it’s all about first impressions, albeit more about reinforcing them once met in person by simply saying their name; although it also may include a hint of gaining a reputation by word of mouth, and other ponies recognize them by how they move. In a pony culture that uses these names, the idea is that you’re looking for some pony that’s doing a specific action often enough. Or rather, you run into them while they are doing it, which if used without a Physical descriptive name reduces the chance they were looking for them and makes it more likely they simply heard of their reputation. This Is painfully obvious a way of looking at things when Rainbow Dash does the whole Crash into Hello thing. These names are probably selected based on a ponies first or most common set of actions while still a Filly as seen by the parent.
Convention Three: Behavioral/Personality Trait.
Fluttershy is the only one of the Mane Six with this convention, with “Shy”, but it’s also potentially Present in Sweetie (Belle) and Cheer(-ilee). And Trixie is a maybe if you consider it a distortion of “Tricky”, meaning she’s a trickster. Unlike the previous naming conventions, these are less focused on first impressions and more on what kind of behavior to expect from them in future. Trixie for example may be a warning light to others that one should expect her to not to be the easiest to live with thanks to her pulling a few tricks on you. It’s kinda like how some villains in other shows are named things that others should run away from really fast, except invoked. This part of the name may be given after much thought unlike other names, after interpreting the young Pony’s behavior and noting it’s fairly consistent. This is one kind of name that doesn’t so much seem to be good for finding a pony while out on the street. But under the consideration of the possibility of meeting them in their natural circumstances while already knowing their name, it is possible for it to boost the first impression more if their first impressions live up to the impression their names gave. The best point on Pony cultures that use these names is that they are probably very intimate.
Convention Four: Objects
Apple(Jack) and (Pinkie) Pie are the two I can think of. But I can’t imagine a proper reason for this type of name so easily. My best guess it has something to do with what they or their family is expected to be able to work with and what they can create. In which case, it’s another one of those names that don’t have anything to do with first impressions, but this time it’s more like their name is a good substitute for a business card. So once everyone is introduced, they know who to go for to get what in that town. I suspect this is one of those names that is simply passed down like a family name, seeing as anyone in that family is likely to pick up some skill that’s been passed down the generations, although in the case of Apple Bloom that may muddy the issue. But whatever the case, pony cultures with these kinds on names seem to be very work oriented.
Well, that’s my over analysis on pony culture for the day. On something completely trivial as names no less. I’ll leave you guys to figure out further possibilities.