わたしと一緒に写真を撮ってもらえませんか？って英語でなんて言うの？

"Could you take a picture with me?" is a more casual expression. I'm guessing that you are sight seeing or maybe you met a famous person and you want a picture with them so you would say: "Hello! Could you take a picture with me?" The other expression: "Would you mind if we take a picture together?" is a more polite expression because we use the phrase "do you mind?" which is used when you don't want to bother that person, specially if they look busy and you want to sound polite. Example: "Excuse me Mr. President, Would you mind if we take a picture together?"

The first two questions are straightforward ways of asking a person to be in a photograph with you. The last phrase is not a question but a suggestion, good for your friends but it may be better to ask for people who you don't know so well.

"Please take a photo with me!" "Would you join me for this photo?" "Would you take a selfie with me, please?

The first two expressions do not specify exactly who will take the photo, but the context of the situation will usually define that - for example, if there is only one camera and it is your friends. The third example asks the person you are with to take the photo. A "Will you take a photo of us together?" B "Sure, can I use your camera? You've got more pixels."

This means that you would like a photo taken together.

"Would you mind taking a picture with me?" is a polite way to ask someone to take a photo with you. 'Let's take a picture." is used a command or suggestion when speaking to someone you know like family or friends.

"Let's take a selfie!' This is a common way to ask someone to take a picture with you. A selfie is a photograph that one has taken of oneself or with another/other people, typically one taken with a smartphone or webcam and shared via social media. "Do you mind if we take a picture together?" You can say this as a way of asking if the other person has a problem with stopping and taking a photograph with you. Can we take a picture together please? This is a casual and polite way of requesting a picture with someone.

~ってもらえませんか = a suggestion ~ってもういいですか = a request If it a request, please use "could you take a photo with me?" or "can we take a photo together?"

Can I get a picture with you? Will you have a photo with me? Would you mind having a picture with me? These are all suitable ways of asking someone to have a photograph taken with you.