In which dialect are 애 and 에 pronounced differently?

Question

I found the following sentence in Duolingo:

Due to recent sound changes, 애(얘) and 에(예) are pronounced the same in most Korean dialects.

However, according to Wikipedia Korean IPA article, the former is [ɛ] while the latter is [e].

I wonder in which dialect they are pronounced the same and in which differently.

Also, how is it treated in Seoul?

And finally, if they are both pronounced the same, how can Koreans distinguish them based solely on hearing them?

Related: Pronunciation differences between 어 and 오, 애 and 에 in DPRK

Answer 1

I wonder in which dialect they are pronounced the same and in which differently.

Older speakers in 서북 방언, 동북 방언, 육진 방언, and 제주 방언 distinguish them according to this paper.

Location of dialects

Also, how is it treated in Seoul?

There is no verbal distinction between ㅔ and ㅐ in Seoul, again, according to that paper.

And finally, if they are both pronounced the same, how can Koreans distinguish them based solely on hearing them?

By memorizing how words are spelled. Your question is akin to asking "how do English speakers distinguish between 'they're' and 'their' based solely on hearing them?".