I don't think Italy needs any special translation apart from 意大利 since it is a single country in the eye of the chinese world and doesn't have the complicated political systems that exist in China, Taiwan, HK and elsewhere. The translation of republic shouldn't be taken literally from modern day understood english names for "China", "Taiwan", "Hong Kong".
1. The official name of Italy in Mandarin.
Italy is short for its official name Repubblica Italiana. Its official name in Mandarin is 意大利共和国. 意大利 is short for 意大利共和国.
It's similiar to 法国, etc. I don't see any reason to miss "republic" out of their offical name in the translations in the official occasions.
The OP was asking whether or not in Mandarin he/she could translate "Repubblica Italiana" as 意大利民国. Since Republic of Korea, 民国 logically stands for republic in Mandarin. The OP was not clear about the difference between 民国 and 共和国。
Since when 中华人民共和国。 = 中华民国 ?
Unless something has changed, in modern times:
中华人民共和国。 = People's republic of China (Mainland China)
中华民国 = Republic of China (Taiwan)
One is a communist country, the other is not.
(1) Since when I say 中华人民共和国 =中华民国？
But I can tell you since 1971 中华人民共和国 has replaced 中华民国 to take seat in all UN organs to stand for China which previously were hold by 中华民国。
Here's the source from the Wikipedia.
(2) 中华人民共和国 = People's repulic of China including Hong Hong S. A. R, Macao, S. A. R, etc.
People's republic of China =/=Mainland China)
(3) 中华民国 =/= 台湾 (Since when Taiwan has declared its independence?) Do you know when 中华民国 was founded? Do you know where 中华民国 was founded? Do you know who was the father of 中华民国？Do you know Madam Song Qingling, the widowess of Dr. Sun, who is recognised as the father of 中华民国 both in Taiwan and the mainland， was a vice chairwoman in 中华人民共和国？
At least more than 140 sovereign nations in the world including Canada government and the UN admit one China only, and doesn't admit 中华民国 de jure. (I don't care that you personally
would like to deny Canada government's recognition about this arbitrarily.)
(4) China is not a communist country. China never claims herself is a communist country, but socialist country. Ruling under a communist party doesn't equal it is a communist country. Please define communism with a reliable source. And it is not a de facto communist country.
Communist party is legitimate in the US. Theoretically their party members have a chance to win the presidency election according to US Constitution. Don't tell me the US will become a communist country if their candidate wins the election.
3. Chinese name of Seoul
Unless i'm mistaken, unlike Pyongyang and Pusan and many other cities in Korea that have a chinese character equivalent, Seoul was always called Seoul in Korea and there never was any chinese character to represent the name "Seoul".
I think the difference in usage of between 汉城 and 首尔。 is purely a Chinese made-up one.
I am sure that Hong Kong S. A. R officially adopts 首尔 when it refers to the capital of ROK since it is subject to P. R. China. You can call up the local consular of Korea to verify it. Tel (852)2529-4141 Fax(852)2861-3699
ROK has officially changed the Chinese translation of Seoul from 汉城 to 首尔。
As to Taiwan, it is de facto not under the governing of Beijing. I am sure Taipei officially follows Korea's request about the name of Seoul in Chinese.
Some folks are uninformed
, so they continue calling it 汉城, which is an obsolete word.
Except for Taiwan and Hong Kong, in Singapore_based Chinese media outlets aslo use 首尔。
P. S. I wound't like to furthur debate the Taiwan issue since it is highly politcially charged and sensitive, and it is not pertinent to the OP's question. If you are still interested in, you can PM me, or start a thread in which you think it is appropriate.