I have started

When I decided to come to New Zealand, I thought that I wouldn't find a lot of Colombian people, but I have found a lot of Latin American people, so it has been become a big problem for improving my English. I like so much Auckland very much but I would prefer to go come back to my country and not stay here for a long time. One reason is because I'm a lawyer in my country Colombia so if I wan't want or decide to stay here, I will have to start again my career again. [Remember that carrera and career are false friends. Do you mean start studying again?]

I have started

When I decided to come to New Zealand, I thought that I wouldn't  find a lot of Colombian people, but I have found a lot of latin american people, so It has been a big problem for me to  improve my English, I like  Auckland so much but I prefer to come back to my country and not stay here for a long time. one reason is because I'm lawyer in my country so if I decide stay here I have to start  my career again.