Unfortunately, when I arrived in Prague, I felt sick. Unfortunately, when I arrived in Prague, I felt sick.

What countries in Europe have you visited? What countries in Europe have you visited?

What countries in Europe have you visited? What countries in Europe have you visited?

First, I have visited UK in the end of the 90´'s, with my school. First, I visited UK in the end of the 90's, with my school.

If you are firmly situating the action in the past, use the imperfect (or past perfect, as needed). The present perfect describes "present" states, so you can't use it when adverbs or adverbial phrases that indicate that it happened in the past. Compare: "I fed the cat yesterday" and "I have fed the cat."

First, I have visited the UK inat the end of the 90´s, with my school. First, I visited the UK at the end of the 90´s, with my school.

You have visited several countries over a long period of time. This particular visit happened only once (because you specified “first”) so you visited the UK.

First, I have visited the UK inat the end of the 90´s,s with my school. First, I visited the UK at the end of the 90s with my school.

Many people, including native speakers, put an apostrophe in 90s, 80s etc, but you do not need one.

We visited London and some cities ofin the south of Englishand. We visited London and some cities in the south of England.

We visited London and some cities ofin the south east of Englishand. We visited London and some cities in the south east of England.

English is an adjective. You need to use the noun England here.

We visited London and some cities of thein south ofern Englishand. We visited London and some cities in southern England.

I visited Bruxellessels, Bruges and Antwertenp. I visited Brussels, Bruges and Antwerp.

I have also visited Italy,. I went to Torino. I have also visited Italy. I went to Torino.

This is a run-on (these are two independent clauses) so you need to either separate them or use a colon or semi-colon (not recommended here since it does not work out logically).

I have also visited Italy,; I went to Torino. I have also visited Italy; I went to Torino.

(This is a very picky correction. It’s not too important so don’t worry about it — it’s even a common mistake for native English speakers!)

I would have preferred to visite Rome, Venisce or Florence, but Torino was findhere we went. I would have preferred to visit Rome, Venice or Florence, but Torino where we went.

When the verb infinitive ends with a single vowel and then a single consonant consonant, you need to double the consonant when adding -ed and -ing suffixes. (Otherwise it would imply a different pronunciation.) So hop → hopped and hopping, but hope → hoped and hoping.

I would have prefered to visite Rome, Venise or Florence, but Torino was finde. I would have prefered to visit Rome, Venise or Florence, but Torino was fine.

My correction now means “Torino was ok”. I’m not sure if this is what you meant?

Finally, iI have visited Czech Republic,. I went to Prague. Finally, I have visited Czech Republic. I went to Prague.

Finally, iI have visited Czech Republic,; I went to Prague. Finally, I have visited Czech Republic; I went to Prague.

Finaly, i haveI visited Czech Republic, I went to PraguePrague in the Czech Republic/Czechia. Finaly, I visited Prague in the Czech Republic/Czechia.

I vomited several times so I was not able to visitexperience the city. I vomited several times so I was not able to experience the city.

You already "visited" the city since you went there, so "experience" (or "get a chance to explore") would be better.