4th Gen Legends, the GTS and the Pokedex

[Psi Yamaneko]

Alright, sorry if this sounds "n00bish" cause, well...I'm not really a n00b.

But here's the thing. In the GTS I see a ton of people who are looking for Mew, Ho-oh, Entei, Groudon and what have you. My question is...how? How could they have SEEN these things so that they could seek them on the GTS?

Is there an upgrade somewhere that gives you Legend sightings? Or...Or did they just manage this with brief trades? Cause that seems like it would be a hassle.

It's just something that's had me scratching my head for a while now. And sorry if this was asked before.

 

[Myzou]

Or, like most people, just want a pokemon of a different language, which is why people do insane trades, such as the dialga I got for an english budew that I put up just so I'd get more search results o.o;