WarcraftRealms.com

With the standard user interface when you mouse over a character you get a tool tip with (if player):
Character name (and title if enabled) and if cross-realm you get " - RealmName"

example " Realms Worst Hunter Manyshots - BurningBlade" {Title and name fictitious.. realm name valid }

My question for you is.. have you any information of other handling of realm names in the tool tip? What you see there is what I can get from the game api calls used in the addon. Unfortunately I expect the only way you will see these realm names is when you are in cross-realm battlegrounds, so you need to be on a server in the same battlegroup. US realms may be able to get this from cross-realm zones.. which apparently isn't yet implemented in EU region.
[Edit].. oh wait.. I forgot the Looking for Dungeon group tool that is also cross realm.

how do these realms show up?
"Azjol-Nerub"
"Blade's Edge"
"The Venture Co"

and really how do these realms show up? (I can only see the names as provided by Blizzard realm status pages.) If they do show as different names for the same realm, I'll need to trap and change the realm names.
EU realms
"Die Arguswacht" a German RP-PVP realm which I believe is called "La Veille d'Argus" only when using the French language pack.

"Scarshield Legion" an English RP-PVP realm which I believe is called "Légion du Bouclier balafré" only when using the French language pack.

US realms

"Nemesis" a Brazilian PVP realm which shows up only in the es_MX Spanish language as "Némesis"

and last but not least how about:

"Pozzo dell'Eternità" the Italian PVE realm which shows up as that when using Italian language everywhere else it is "Well of Eternity"

I'd find it hard to believe that the realm names change language according to what language pack you are viewing them in, I'd be interested to learn where you've heard that! I can certainly tell you the realm list ingame does not translate the names, and they all show as the actual name when you're logged in on them (else I couldn't census anything other than English realms), so if tooltips change, that would seem very strange indeed.

Have never come across any of these names so far anyway, since the different language realms are separated for LFR/BGs, etc, not sure about the Italian realms, given there's only two of them, but the only time I (on an English realm) would ever meet someone from French/German/Spanish realms, is if someone grouped with them via RealID/BattleTag and so pulled them into an English realms group (or onto my server in crossrealm zones), which is likely to be pretty rare.

That being said, RealID is handy for testing purposes, borrowed my other half's account to form some crossrealm groups with my census alts... The following are all as shown in ingame tooltips, tried to hit as many potential problems (punctuation, spaces, languages) as I could:

Al'Akir
AzjolNerub
TheVentureCo
Blade'sEdge
ZirkeldesCenarius
CultedelaRivenoire
Pozzodell'Eternità

Well, Pozzo dell'Eternità was weird - "You have invited Census-WellofEternity to join your group", but when in the group, the tooltip shows "Pozzodell'Eternità". Strange one! However, hopefully an indicator that tooltips at least, go by the ingame name and are not translated... hopefully!

I can not be entirely sure if I recall correctly, but I seem to have read in some official forum post that the two Italian realms are still technically part of the English server groups. If that vague memory is correct, it would account for the strangeness Balgair encountered.

Balgair wrote:I'd find it hard to believe that the realm names change language according to what language pack you are viewing them in, I'd be interested to learn where you've heard that!

Well I have to admit it is just a guess, but if you go to the web side Realm status page and use the delimiters "RP PVP and German" you will see 6 realms.. if you change the language of the web page you will see that the French page changes one of the realm names.

Ditto with the other two realms I mentioned.

At this point it time... I'm trying to protect the WR database by capturing and translating (where different) realm names to the standards used by Rollie. (other then his miss spelling of the Italian name.. that needs to be fixed!)