Question

why did scientists struggle for thousands of years to accurately describe the solar system?
venus has phases like the moon.
many people spoke italian and did not understand latin.
the planets appeared to move backward in the sky occasionally.
scientists could not explain why the sun appeared to rise and set every day.

Explanation:

The retrograde motion of planets (appearing to move backward in the sky) was a major challenge for early - astronomers trying to accurately describe the solar system. Venus having moon - like phases actually supported the heliocentric model. Language differences (speaking Italian and not understanding Latin) are not related to the difficulty of describing the solar system. The rising and setting of the Sun can be simply explained by the Earth's rotation.

Answer:

The planets appeared to move backward in the sky occasionally.