Yeah, i use gaelic for quite a few of my toons when appropriate. I dont RP, but yeah for the most part they have to sound like names that fit the character (and sound at least a little badass).

My NE rogue = Cyno = My handle for ~15+ years.

My Draenei shammy = Tsyanis = Tibetan for fear, another old handle for when Cyno was unavalible.

Hooman dk = Dubhlann. = Gaelic for ebon blade. Well, ebony blade. Well... negro blade, technically.

Worgen huntard = Cascorrach = Mythological irish king who killed werewolves.

Bank alt = Airh = Gaelic for gold.

BE huntard = Daoine = gaelic for elf sorta.

Goblin lock = Gandino = italian goblin creature from mythology.

And i have my panda name all reserved. Chengdan = chinese for bear, very simple.

Hi native gaelic speaker here from Ireland and just wanted to correct some of your words!
Óir is gold.
Daoine means people.
Dubhlann means black pool/lake and is the old old name for the capital of Ireland -Dublin, the modern Irish name is Baile Átha Cliath.
Airh is now aire and means shepard but it can also be used as the verb 'to take care of' i.e i took care of my sick Worgen friend during the full moon = thug mé aire do mo tinn chara worgen nuair a bhí an geallach lán.
Hope this clears stuff up for you :)