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How do Icelandic and Faroese pronunciations preserve diphthongs?

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Scandinavian languages Distribution of the Germanic languages in Europe.

In Icelandic and Faroese, the preservation and development of diphthongs are distinct from the evolution seen in other Scandinavian languages. While original diphthongs from Old Scandinavian became long vowels in languages like Danish and Swedish by the 10th century, Icelandic and Faroese have maintained a rich system of diphthongs through different linguistic processes.1

In both modern Icelandic and Faroese, long vowels have undergone diphthongization. This means that sounds that were historically simple vowels have evolved into diphthongs in these languages. Examples of this include:

Icelandic: Long vowels such as é (pronounced /je/), ó (/ou/), á (/au/), and æ (/ai/) are realized as diphthongs.1
Faroese: The language is particularly notable for its many diphthongs, which developed from older, simple vowels, such as í (/ui/) and æ (/æa/).12

Essentially, rather than losing the diphthongal character of the language, these two tongues have actively developed or preserved complex vowel sounds that distinguish them from their North Germanic relatives.12