Introduction
Howdy all.
After the nightmare that is the question-fest in the comment section of the Japanese Shiny Tapu Koko,
I decided to take my time to write this, in hopes that it will shed light on some questions surrounding this, and also future events.
Groundwork in terminology
To ensure we are all on the same page, some refresher on the terms that will be used.
3DS region refers to the region that your 3DS belongs to, named as per seen in your system settings page.
Examples inside:
Game Save Language refers to the language you selected at the start of the game.
Wonder Card Language refers to the language of the wonder card, identified by the distribution text and distribution title.
That is how our wonder cards are categorized in our Event Gallery.
Pokemon Language refers to the language of origin of the Pokemon itself.
Most wonder cards are programmed to have the generated Pokemon follow the Game Save Language,
as opposed to the Wonder Card Language.
Region locked: Event redemption (usually code) only redeemable on that one region.
Region Free: Event redemption not restricted by regions.
Region Expanded: Event may allow multiple regions, but not all.
Now that we are all caught up, more reading!
Types of distributions in Generation 7
Right now, these are the primary types of distributions, and how they are categorized:
Serial code - Region locked or region expanded
Local Wireless - Region Free
Nintendo Network - Region locked
An example of such a scenario is the Lunar Shiny Magikarp.
Also, it appears that for HKTW unique distributions, you can only receive the distribution on EU 3DS,
If your game save language is ENG, JPN, KOR, CHS or CHT. (thanks @Kirzi )
[meaning otherwise, you won't be able to receive the wonder card]
Region locked options
The simplicity of Local Distribution events
Most, if not all, of Local Wireless and Infrared Region Free events only broadcast the wonder card in one language,
which is normally the native language spoken in that country.
Example, events held at Mega Tokyo Pokemon Center in Tokyo, Japan usually have Wonder Card Language as JPN.
Events held in some mall in South Korea usually has Wonder Card Language as KOR.
And since these events are Region Free, you can go and receive them on any 3DS region.
Don't get duped by the Language Tab in a summary screen
Ah, that black box that is the stuff of nightmares.
During the release of the JPN Tapu Koko, people thought that only one that bears the "JPN" can be legit.
WRONG.
The language of the Pokemon (that we know is generated by Game Save Language) isn't the same as 3DS Region.
It'll show up as long as language of Pokemon is different from game save language.
Here's an example of the Legal Tapu Koko.
As you can see, name and language is ENG, language tag doesn't appear (because game save language is same as PKM language),
and 3DS Region is JP, meaning it's completely legal.
It is possible for an event to force the pkm language to match the wonder card language, but so far it's only done on Ash-Greninja.
Always be aware if the event is Region Locked, and whether it forces the Language of the Pokemon to follow Wonder Card Language.
PS: PKHeX isn't programmed to deal with region locked events, as the wonder card themselves doesn't show whether it is region locked.
So you may have a Pokemon with the wrong region, and PKHeX wouldn't correct you on it.
Conclusion
And there you have it. I've imparted all the knowledge I know regarding this.
Make good use of this information.
I'll give you a potato for surviving this long post, but I can't.
Feel free to ask questions,
However, anyone who posts questions that have the answers in this,
(basically giving me the impression that you didn't read this)
shall be royally punished.
Haven't thought of how. Do we have any form of community service here, I wonder?