Learn Italian: I lunghi oblii rovinano gli oggetti. - Long oblivions ruin the objects.

This comes down to where the stress falls in the singular noun. In oblio (oblivion), the stress is on the i (oblìo). When the i in an -io ending is stressed, the plural takes a double -ii. For words like orologio or viaggio, the stress is elsewhere, so the plural just drops the final o and leaves a single -i.

How do you pronounce the double ii at the end of oblii?

Because the first i is stressed, the two vowels are actually pronounced as two distinct syllables (oh-BLEE-ee). However, in normal conversational speed, it often sounds like a single, slightly lengthened "ee" sound.

Why is there an h in lunghi?

The singular adjective is lungo. To make it masculine plural, the o changes to i. If we just wrote lungi, the g before the i would make a soft "j" sound (like in the English word "gem"). We insert the h to maintain the hard "g" sound (like in "go") from the singular form.

Is it normal to use a word like "oblivion" in the plural in Italian?