It’s a bit simpler than that. If you have not released a game in a certain country, it is not available to purchase in that country. These days, you can always import it, through eg. Amazon, but you won’t find it in any retail or digital store. Before the prevalence of online retailers like Amazon, importing was a much more difficult prospect.
Note that imported copies of console games from another country may be region locked, meaning they only run on a console manufactured for that region, so you would also need to import a whole console just to play that game. These days region locking is artificial, mostly for business reasons, but in ye olden days, it was (also?) for technical reasons, due to the differences between NTSC and PAL televisions. You might have needed to import a custom television set while you were at it.
In the case of Halo 2 specifically, however, the information you linked to is incomplete. The date listed for release in the US is actually its release date for all of North America, including Mexico. See here:
Whether it has localization is up to the developer/publisher, and is not necessarily related to releasing it in a certain country/region.