i've taken the iPhone 5 to each of those countries without really much of a problem. however, i was traveling on a global corporate plan so data consumption was not too much of a problem
i've tried the Lumia 920 in Taiwan before and did not like it very much
from an iPhone perspective...
- mophie juice pack. this was by far the best traveling investment i've made. foreign countries + constant Google maps searching is a quick way to drain the battery
- invest in a global data plan. in Italy, Wi-Fi hotspots are quite scarce and almost all of them charge for access. i'd take a hard look at T-Mobile's everything + unlimited global plan for $70 a month or find a local pay-as-you-go service. in China and Japan, their large carriers usually have retail shop everywhere so just pop in and get a pre-paid SIM. usually they ask for two IDs (e.g. USA passport and drivers license)
- navigation. offline nav will not work well. if you online, Apple / Google maps was passable in Italy if my memory serves but i'd always confirm directions with the hotel concierge. in Asia, both of those map applications were hit-or-miss in my experience... especially if you have to use the local language as the search input. in Sweden it was pretty decent. given the high fluency in English there, even if the maps don't work asking for directions is fairly straight forward. depending on where you're going in Japan / China, you may be better served by getting a rail map + phone map
i have not touched my Lumia over have a year now so i do not know what's been updated... however i do remember the maps was severely lacking when i was in Asia
What phone would be better when taken in consideration traveling to europe and asia?
I'm going to be in Rome for 2 months, and Sweden for about 6 months... besides that i will be in the United States. Might make a trip to Japan or China too.
The two phones I'm looking at: Lumia 1020 or iPhone 5S
Taking into account:
-Navigation - OFFLINE navigation needs to be strongly considered... including finding bus routes, where you are, street views, walking, restaurants, attractions, etc.
-Battery life
-Camera