Translation:August and September are months of the year.
Paulenrique is right. But notice that (as long as I can tell) most of the audio for Portuguese has an accent usually found in big cities like São Paulo and Rio de Janeiro. That is why it sounds like "chee".
And as you may tell, the accents vary depending on the region. For example, people in Curitiba (the capital of Paraná state in the south region) will say "leiTE", "noiTE" and "quenTE" as opposed to what you hear in the Duolingo lessons (the /chee/). As you go north, it becomes more like "tee" (like English word Tea), instead of "chee".
Your question reminds me more or less the eternal debate over the right spelling of "tomato" and "either".