あいづちって英語でなんて言うの？

"Mmhmm" is not actually a word, but more of a sound that is made, it is loud enough to be heard and it lets the speaker know that a) you are listening what they're talking about and b) they should continue. And although it is loud enough to be heard, it isn't so loud that it makes the speaker stop speaking. It simply affirms your interest. You may use this while someone is explaining something to you, or telling you a really long story. "Oh wow" is said when something surprises you and you want the speaker to continue. Usually this is used when you are being told an interesting story. "Yeah..." When saying this word you may drag it out a little bit. It shows the speaker you are engaged in whatever is being spoken about and are paying close attention. This can be used when someone is telling you something suspenseful.

To give positive confirmation of agreement or understanding.

Yes, yes..and Uh-huh are " polite interjections" that we often use to show we are listening. It suggests...affirmation, agreement, or gratification in the English language. We usually also nod the head at the same time to and "show agreement". Mmmm Uh-huh Yes ...Wow...really? All of these are " interjections".

We would call these phrases feedback or acknowledgement to show that what is being said has been understood. You can also say: I get it. Ah. I hope this helps!

You can say : 'I understand' 'I see' 'I get your point' 'Exactly' 'Yeah'

This is called showing interest... >That's fascinating... >Do tell me more >Really? >Yep... >Okay...