If I said that I'm an atheist in your nation?

[Regiria]

If you're an atheist, you're an atheist.

[Poatosl]

If you said you're an atheist in my country you'd be burned at the stake

[The Sakhalinsk Empire]

If you're an atheist, you're an atheist.

Same here.

[Ieskarios]

People would shake their heads, or say a prayer for you, but not much else.

[Telario]

In 2006, a law came into power to give tax credits to atheists to discourage religion in Telario.

[Agonya]

That's your problem but you're still going to Hell.

[Kaniros]

They might think you're stupid for not believing the existence of gods that have proven their existence in Kaniros although nobody would care much as Kanirosians despise gods, which is why they have a special force just for hunting and destroying gods.

[Levante Oriental]

It depends of our leader whims. Our leader could praise you or sending you to a detention camp is She has the period.

[Egyptosian]

we will gladly accept you into our population

[Comhghall]

You'd most likely be executed. Atheism is viewed as a mental disorder and a dangerous condition.

[Lux Pulchrae]

No one would talk to you, maybe even refused service at some businesses

[Sarcana]

The government’s reaction

---

Nothing would change how the government treats you, as atheism is completely legal and even the majority amongst the public.

The public’s reaction

---

Very few people world care, but that minority may be either relieved or agitated. Atheism is the majority within Sarcana, and so it is often that others are pleased when they hear one is not religious.

The religious folk on the other hand would likely just ignore you and try to avoid you.

[Liburia]

There would be no problem, 15% of Liburians are irreligious and the rest are quite tolerant.

[Lerova]

No one would care. Approx. 5% of Lerovan are irreligious, and the rest are religious, but highly tolerant.

[Mangahhan Super Region]

Simple, You will be arrested!

[Oncolithia]

They would instantly be converted into Christianity, but here's the twist: they can deny the conversion if they want to.

[Lethage]

The founding of Lethage is directly bound to the Lethaginian Gods. Being an atheist is not a problem by itself, but in Lethage, only an unpatriotic person would be an atheist, and the lethaginian people really dislikes unpatriotic dudes, so they might beat you up in the streets. The government doesn't approve this behavior, but does not condemn it neither, so you better watch your tongue while you're here.

[Greater Korean Juche Republic]

You would be viewed as normal.

[The Canus Empire]

Of course, my people may not like or encourage atheists in our nation, they will be fine and let you be! Well that is what I hope.

[Elvectica]

Atheism is fairly popular, however the freedoms in place let you be protected against hate crimes against beliefs that others may find 'heretical'

Since Elvectica is the epicentre and cultural hub of the omniverse and those of infinite dimensions, there's quite a few LOT of weird alien religious beliefs.

[Crookfur]

The general response from most Crookfurians would be to shrug and say "whatever mate".
You will still get invited to church celebration type events such as christenings and weddings and likely repeatedly be told that you are very welcome to attend services if you want. They wouldn't even really be trying to convert you but are just being welcoming and nice.

Of course there are a few rougher areas where such a declaration on being questioned is the same as choosing the tin can option in response to the question "Are you a Billy or Dan or an auld tin can?" and as such gangs of both persuasions will give you a light battering for failing to take part in their tribal/territorial games.

[Andower]

It's unusual (around 80% of people here claim to be religious) but becoming more common. You wouldn't face any serious social consequences from most people for declaring your atheism.

[Donnegall]

You would be arrested and deported to the Republic of Ireland, a reportedly arch-Catholic nation obviously full of atheists. You would belong to there, not to Donnegall.

[Baudevaux]

Everyone around you would continue whatever it was they were doing. If someone was feeling particularly generous with their time, you might get a shrug and a disinterested grunt.

[Neonix]

Nobody would care.

Correction: the select few people who think they know everything and that everyone else is moron would care - either due to disagreement or in some kind of self-congratulatory "me too" way.