Here, in the North, 40% of the population consist of Russians by 40%is Russian.

I've never gone abroad in my life.

My nationality isI am Kazakh.stani

"My nationality is Kazakh." works, but "I am Kazakhstani" sounds more natural.

I live in a town near the capital city, which is now called Nur-Sultan but it's been, which was called Astana until 2019.

The population of our country, that is nearly 18 bmillion people, is rather small for the country which isgiven it is the 9th biggest country by landmass in the world.

I removed "which is" from inside the commas because that makes it sound a bit less repetitive. For example, the wikipedia page for Kazakhstan starts with "Kazakhstan, officially the Republic of Kazakhstan...", instead of "Kazakhstan, which is officially the Republic of Kazakhstan..."

Also, a billion is 1,000,000,000, and a million is 1,000,000!

My first is language is Russian.

Here, in the Nnorth, 40% of the population consist ofare Russians by 40%.

Historically, this proportion was even bigger, so it's not a surprise, that there isare more Russian schools than Kazakh schools.

Moreover, I haven't been to many cities in my country, just in a few of them.

My dream is ridingto ride on bicycle around Kazakhstan and maybe, other former USSR countries, like Russia and Ukraine.

Thanks for reading this and I'll be grateful for fixingany mistakes you fix in the text.

I was born in Kazakhstan and I've lived all my life in Kazakhstanhere.

Sharing prepositions isn't unacceptable, but here, since the second part has a long adverbial phrase attached to it ("all my life"), it sounds awkward.

I live in a town near the capital, which is now called Nur-Sultan but it's beenwas called Astana until 2019.

"Has/have been" is used to describe a current state that persists from the past, not a past event per se. For example:

Past perfect:
- "Did you eat yet?" "Yes, I've eaten."
- "How long have you lived in Paris?" "I've lived there since 2006."

Not past perfect:
- "Did you eat lunch yesterday?" "Yes, I had lunch at work."
- "Did your late father write a will?" "Yes, he wrote a will."

The population of our country, that is nearly 18 billion people, is rather small for thea country which is 9the ninth biggest country by landmass in the world.

"By landmass" makes what you're trying to say clearer.

My first is language is Russian.

Maybe it isn't that obvious, but in Nnorthern Kazakhstan, people mostly speak itRussian, especially in cities.

Here, in the North, the population consist of Russians by 40%Russians are 40% of the population.

Or:
- Russians constitute 40% of the population.
- The 40% population is Russian.

"Consists" is more appropriate when talking about the make-up of something as a whole:
- "This consists of X$ of A and Y% of B."
- "The population consists almost entirely of immigrants."

Historically, this proportion was even bigger, so it's not a surprise, that there isare more Russian schools than Kazakh.

Moreover, I haven't been to many cities in my country, just in a few of them.

My dream is riding onto ride a bicycle around Kazakhstan and maybe, other countries of the former USSR countries, like Russia and Ukraine.

"Former USSR" countries is correct, but this sounds more natural to me, as it's a more typical phrasing.

Certainly, I want to visit some more distant countries, maybe the USA, France, the UK or Scandinavian countries.

Thanks for reading this and I'll be grateful for fixing mistakes inany corrections to the text.

I live in a town near the capital, which is now called Nur-Sultan but it's beenwas called Astana until 2019.

The population of our country, that is nearly 18 billion people, is rather small for thea country which is the 9th biglargest country in the world.

Here, in the North, the population consists of Russians by 40%.

'Here in the North' is a simple phrase, so you don't need the first comma.

Historically, this proportion was even bigger, so it's not a surprise, that there isare more Russian schools than Kazakh.

Moreover, I haven't been to many cities in my country, just in a few of them.

My dream is riding onmy bicycle around Kazakhstan and maybe, other former USSR countries, like Russia and Ukraine.

Alternately: 'My dream is to ride a bicycle around...'

My cCountry

Titles should be capitalized

I was born and I've lived all my liferaised in Kazakhstan.

What you said is technically correct, but it is way more common to hear "born and raised"

I live in a town near the capital, which is now called Nur-Sultan, but it's been was called Astana until 2019.

The population of our country, that is nearly 18 billion people, is rather small for the country which isconsidering it is the 9th biggest country by land in the world.

You didn't need the "that is", so I got rid of it.
I reworded the rest of the sentence to make it sound smoother. I added in "country by land" because otherwise, it would've been unclear. For example, you could have meant that Kazakhstan was the 9th biggest country by population.

My first is language is Russian.

Here, in the North, 40% of the population consists of Russians by 40%.

Sounds smoother this way

Historically, this proportion was even biglarger, so it's not a surprise, that there isare more Russian schools than Kazakh.

"larger" sounds better here than "bigger"
I changed "is"to "are" because "schools" is plural

Moreover, I haven't been to many cities in my country, just in a few of them.

My dream is riding on a bicycle around Kazakhstan and maybe, other former USSR countries, like Russia and Ukraine.

Thanks for reading this, and I'll be grateful forhappy to fixing mistakes found in the text.