I a'm Carlos, and I have'm 34 years old. I'm Carlos, and I'm 34 years old.

Saying "I'm [name]" is more on the casual side, which is why using the contraction "I'm" is more natural Alternative (more formal): My name is Carlos

I am Carlos and I haveam 34 years old. I am Carlos and I am 34 years old.

I am Carlos and I haveam 34 years old. I am Carlos and I am 34 years old.

I live in an apartament in Barcelona. I live in an apartment in Barcelona.

I live in an apartament in Barcelona. I live in an apartment in Barcelona.

I have three sisters and two brothers. I have three sisters and two brothers.

I have three sisters and two brothers. I have three sisters and two brothers.

I have three sisters and two brothers. I have three sisters and two brothers.

I want to learn English because my eEnglish is not very good. I want to learn English because my English is not very good.

A bit more natural to say "not very good." The "very" softens the tone a little bit

I want to learn English because my eEnglish is not good. I want to learn English because my English is not good.

My mother´'s name is Luisa, and we live together. My mother's name is Luisa, and we live together.

Barcelona is a nice city for going out to eat and visiting. Barcelona is a nice city for going out to eat and visiting.

Barcelona is a nice city for got to eat and visivisiting and going out to eat. Barcelona is a nice city for visiting and going out to eat.

Saying visiting first and then "going out to eat" makes more sense because you visit first and then go out to eat.

Barcelona is nice city for going out to eat and to visit. Barcelona is nice city for going out to eat and to visit.

I want to travel a another´s countriesy, but the problem is my eEnglish. I want to travel another country, but the problem is my English.

"Another" does not need a/an before it, since the "a" is actually built into this word (an + other) However, "another" is singular, so if you want to reference multiple countries, rewrite as "... travel to other countries"

I want to travel a anto other´s countries but the problem is my english. I want to travel to other countries but the problem is my english.

"another's countries" implies you want to visit specific people in other countries.

I want to travel a anto other´s countries but the problem is my eEnglish. I want to travel to other countries but the problem is my English.

I must to work more/harder. I must work more/harder.

We often say "work harder" instead of "more," when it's about effort

I must to work more (harder). I must work more (harder).

Harder would sound good too.

I must to work on it more. I must work on it more.

Only I can trustI have to trust myself / It's up to me. I have to trust myself / It's up to me.

A couple of more natural phrases

Only I can trust meyself. Only I can trust myself.

Not sure what exactly you meant here, but it's grammatically correct.

Thanks, see you tomorrow. Thanks, see you tomorrow.

Thanks (or thank you), see you tomorrow Thanks (or thank you), see you tomorrow