I don't really know why this is a big deal... Almost every single character from ATLA had a meaningful name of some sort:
* Zuko in Chinese means "conceited, proud of one's self", which seemed to fit his character rather nicely for a good portion of the first half of the series. Zuko is written as "Resurrected Rule" or "Reclaimed Honor", though another time it was "Ancestors' Robber" on a wanted poster. It is logical to assume that his parents originally used the first "spelling", given that he was a royal child, and his father changed the "spelling" for the wanted posters to indicate that he had been disowned. In Japanese, Zuko also means "sound of swishing swords", though that's probably a coincidence as its an onomatopoeia.
* Piandao is named after a type of Chinese saber (though not the type he used, which is a jian).
* Taking into account the Chinese characters used to write his name on the title card in "Tales of Ba Sing Se", Aang's name seems to mean "Ascending Peace".
* Katara's name comes from a possibly phoenitic word of perhaps the same word, which means "beautiful." The individual parts of the name mean "block", "pagoda", and "pull."
* Toph's name has several meanings: it is a kind of sandstone, and on her passport in "The Serpent's Pass" her name is written to mean "supported lotus", which is indicative of how her parents saw her, as a fragile china doll. Conversely, on the title card in "Tales of Ba Sing Se" her name is written to mean "entrusted man".
* The baby that the Gaang help deliver, who was given the appropriate but out of place name "Hope". The DVD Commentary said it was supposed to be a Chinese name that meant "Hope", but then either the meaning would be lost.
* The Earth King's name, Kuei may be a transliteration of two words different words that respectively mean "chief" and "puppet", where as his Evil Chancellor Long Feng's name means "Dragon Phoenix", which in Chinese tradition represented the throne.
* Both Monk Gyatso's and Tenzin's names come from the current Dalai Lama. (Well, strictly speaking, Gyatso is the name of all Dalai Lamas, and Tenzin is his personal one.)
* The north pole's princess and Sokka's first love interest Yue has a double meaning as well, being in Chinese a word for moon, due to her being reincarnation of moon's spirit and in Japanese meaning a sad incident and used for children dying shortly after birth, such it might have happened to her, due to her being weak at birth.
* Bumi means "Earth" in Indonesian. (Much more relevant to King Bumi than Aang's son.)
* Though in-universe she was named for Fire Lord Azulon (who himself was named for Azulong, a Chinese constellation), Azula is a derivation for "azul", the portuguese and spanish version of "blue", which is appropriate as most of her firebending techniques are that color. Furthermore, it has been said that Azula was originally going to be "Prince Azul," before the Avatar folks decided to make her female.
* According to the Avatar wiki, Ozai's name can mean either "leisurely year" (he spends a lot of time ordering others around from the comfort of his palace) or "flaming calamity".
* In Mandarin, Zhao means "to look / search for (someone)"... and what does Admiral Zhao do throughout the first season?
* Wan Shi Tong introduces himself to the Gaang as "He who knows ten thousand things" - which is literally what his name means in Mandarin.
Having a nerdy Airbender fanboy named Otaku fits rather nicely.