English. Проверьте на наличие ошибок. Писала сами, без переводчиков. Мне 30, не школьница. Спасибо!

4. This summer is VERY cold. (much не нужно) / It is very cold this summer. Если нужно усилить, то It is extremely cold.
5. They think that they will have to stay IN that country for about a year.
6. Look at the small house with a green roof across the river. (если крыша упоминается впервые, то a green roof, the house если он единственный с зеленой крышей в поле зрения, если нет -- то a house, "на том берегу" чаще говорят across the river)
8. He always has lunch at this time. (не нужно is)
9. He was in China several years ago but at that time he didn't know Chinese yet. (не нужно 'a', вместо at that time, когда речь о прошлом, в разговорном языке можно сказать back then)
10. By this time tomorrow, I will already be in London. (если к этому времени человек будет в Лондоне) . I will have already been in London -- "я уже побываю в Лондоне". Видите разницу? Это потому что глагол be статичный. А вот если бы был arrive, то да: By this time tomorrow, I will already have arrived in London (уже приеду в Лондон) .
12. I went to the park early in the morning 'cause I KNEW that at that time there WERE very FEW people there. (согласование времен, согласование по числу и few, иначе речь о маленьких людях) Более идиоматично сказать: I knew there would be very few people there (так называемое habitual will/would, когда говорят о вероятном событии или ситуации, исходя из опыта или общих представлений) .
13. These are my notebooks and THOSE are yours. (противопоставление, даже если тетради рядом)
14. He's going to work a lot on English (или on THE English language) this year.
15. I was in Sochi in THE summer of 1946.
17. He HAS lived in BULGARIA for very long. He knows that country very well. (если человек по-прежнему там живет, или если он только что оттуда уехал, в противном случае He lived in Bulgaria ...).
18. I'll go to see him at eight o'clock. (все правильно, если намерение возникает во время разговора) I think, I will catch him AT HIS PLACE (у него дома, неважно, здание или квартира) at that time. At his house -- в или рядом с его домом (зданием) . In his house (в его доме) . Если человек запланировал навестить до момента разговора, то I'm going to see him at eight o'clock или I'm seeing him at eight o'clock. Going to go -- не ошибка, но лучше избегать.

is talking with - is talking TO
This summer is coldly very much. - полная ерунда, This summer is very cold.
They are going to go to Poland - They are going to Poland
at that country - in that country
Дальше другие товарищи поправят.
Там есть что.

1. I have been to Odessa this summer.
3--ий не поняла. Дайте русский вариант.
4. This summer is very cold.
5. They are going to Poland very soon. They think they will have to stay there for about a year.
6. Look at the small house with green roof on that bank. I was born in that house.
7. This is my dictionary and that is yours.
8. I don't want to call him. He always has lunch at this time.
9. He was in China several years ago but at that time he didn't know Chinese yet.
10. Tomorrow by this time I will have already come to London.
11. Someone wants to see you. I've never seen this man before.
12. I went to the park early in the morning cause I knew at that time there was very few people.
13. These are my notebooks and those are yours.
14. He's going to work a lot on his English this year.
15. I was in Sochi in the summer of 1946. That summer was very hot.
16. I'm not going anywhere this summer.
17. He has lived in Bulgaria for very long. He knows that country very well.

" I like that city very much." тут местами перепутали слегка, I like very much that city.
7. This is my dictionary and this is yours. - тут не понял что имелось виду, "мой словарь - твой словарь. (Mine dictionary - yours dictionary.)"
или же "Это мой словарь, а это твой. (This is my dictionary, but this is yours.)" в 13 предложение то же самое.
 15. I was in Sochi at(тут надо употребить in) summer of 1946. That summer was very hot.
17. He lived in Bolgary(страна - Bulgaria) for very long.
8. I don't want to call him on the phone. - I don't want to call him.

п. 4 - я бы написала "is very cold".
п. 7 - and that is yours.
п. 9 - уберите "а" перед several years
п. 10 - in this time I will be already at London
п. 12 - there were very few people
п. 13 - those are yours
п. 17 - Bulgary

по мне вроде все нормально