「日本では、電車内での通話はマナー違反とされています」って英語でなんて言うの？

In Japan, speaking on a cellphone on the train is considered bad manners.
は別に不自然だと思いませんが、もっとシンプルな言い方はこのようにできます：
In Japan, it's rude to speak on the phone on the train.

「～はマナー違反とされています」の言い回しで、
「～するのが失礼です」の[it's rude to +動詞の原形]にしました。
また、cellphoneただのphoneだけにしても大丈夫です。

今回は "while" を使ってみました。
【while S＋V】で
【SがVしている間】または
【SがVである一方】の意味です。

➡while you're on the train で
”あなたが電車に乗っている間は”
の意味ですね。

If you wanted to explain that in Japan, it's considered bad manners to talk on the phone in the train, you could express this by saying either of the following: "In Japan, speaking on a cellphone on the train is considered bad manners" or "It is not a good idea to speak on a cellphone on the train, In Japan it is bad manners".

Yes, your sentance does sound natural. I've included some alternative versions you could use.

'Rude' and 'impolite' are very similar, and you could use either. You could also suggest that someone had 'bad manners' meaning that they flout convention as to what is considered polite.

'Considered', in this case, means the same as 'most people think'. Not talking on a phone whilst on a train is thought to be bad manners by the majority of people.

When you want to explain that in Japan, it is considered bad manners to talk on the phone in the train; then you may explain this in the following ways:
-In Japan, speaking on a cellphone while on the train is considered bad manners
-In Japan, it is considered bad manners to speak on the phone while on the train

The example sentence that you provided can be used given the correct grammatical structure however there are many ways in which you can say this. As you can see from the first example, we can also say, "In Japan, talking on your cellphone on the train is rude," and use the word, "rude," rather than, "bad manners."

Western cultures are very different from the Japanese culture. We don't see it as rude if somebody is talking on their mobile phone while travelling on the train. Although, if the person were screaming very loudly or having an argument then yes, it would be considered quite rude and everybody would get annoyed.

Advising someone of the perception can bring light to the situation. Many people in other parts of the world may not believe that cellphone usage is rude. Letting visitors know of such practices can be helpful and keep down looks and rude behaviors.

Both of these options are natural but perhaps the second one is more formal. Etiquette means what is considered polite in a certain society or group.
You could make the sentence as simple as 'it is rude to talk on the phone when you are on a train' or you could add extra details on such as 'it is considered rude in japan'...

Examples:

It's considered rude, to speak on your phone whilst on trains in Japan.

Try to avoid taking phone calls when you are on a train in Japan, this is considered to be bad manners.

It's impolite to use your cell phone for phone calls whilst on trains in Japan.

The two sentences you see provided above are great to express to your listener that speaking on a cellphone while on the train is considered bad-mannered in Japan. In the first sentence you will see the word rude and in the second sentence you will see the word impolite. Both of these words mean bad-mannered. These would make terrific additions to your vocabulary.

First answer: Rude means impolite or bad manners, in other words, it is the same expression as the second answer that I put on there. The only difference is that the first answer is more direct than the second, to be spoken to a friend or a person of high trust.

The third answer has the expression "frowned upon" which means people will frown :( instead of smile :) at you. This is also understood to be considered bad manners.

Use the phrases "It's rude to..." or "It's impolite to..." when you want to talk about something that is not nice or appropriate to do in another country.

It is considered rude to speak on the phone on the train in Japan.
In Japan it is considered rude to speak on the phone on the train.
Speaking on the phone on the train in Japan is thought of as rude.

When you want to let someone know that speaking on the phone whilst on the train is rude, then you can use one of these three sentences.

I hope this helps.
Have a great day.
Will

Rude - offensive or not polite
Speaking on the phone/ talking on the phone/ having a phone-call

It is good to inform travelers of customs in your country.

In the first example, by saying "we don't," it shows that it just isn't the done thing it's not the social norm.
Intrusion - Intrude - to rudely come into a situation - like to intrude into a conversation.
Respecting personal space - we respect a person's space around them and also we're careful about what we say or do in their hearing so as not to offend them.

1. In Japan, talking on your cell phone on a train is in bad taste.
   "In bad taste" means that something is considered offensive
   or inappopriate. It is regarded as an invasion of privacy if others
   are forced to listen to your private conversation. This shows a complete
   lack of respect to your fellow passengers.

2. In Japan, talking on your phone in a train smacks of disrespect.
   Another way of expressing this is to say that it will not be viewed in
   a good light. Basically it means that your fellow passengers will look
   at your behavior as impolite and disrespectful. If something "smacks
   of disrespect" then it means that it displays rudeness and a lack of
   manners.