Complex sentence: Nasal vowels are found in many languages, and in a large subset, such as French, Portuguese, Breton, Polish, as well as in several other language families outside Europe, they contrast with oral vowels.
Split into simpler sentences: Nasal vowels are found in many European languages, such as French, Portuguese, Breton, Polish. In these, as well as and languages found in other language families outside Europe, nasal vowels contrast with oral vowels.