Irse a or ir a - is it a question of context?
My spanish language partner corrected a sentence in one of my emails from: Susan y yo vamos a con unos amigos para tomar un café. To: Susan y yo nos vamos a encontrar con unos amigos para tomar el café. My english sentence/thought was: Susan and I are going to meet some friends for coffee.
Why would a native speaker use "nos vamos a" and not "vamos a" in this case? The context was I was explaining why I couldn't speak with my language partner at a certain time.
Any help would be appreciated.
Thanks.I've just realised there's a mistake in my first sentence. It should read: Susan y yo vamos a encontrar con unos amigos...

Question

Irse a or ir a - is it a question of context?
My spanish language partner corrected a sentence in one of my emails from: Susan y yo vamos a con unos amigos para tomar un café. To: Susan y yo nos vamos a encontrar con unos amigos para tomar el café. My english sentence/thought was: Susan and I are going to meet some friends for coffee.
Why would a native speaker use "nos vamos a" and not "vamos a" in this case? The context was I was explaining why I couldn't speak with my language partner at a certain time.
Any help would be appreciated.
Thanks.I've just realised there's a mistake in my first sentence. It should read: Susan y yo vamos a encontrar con unos amigos...

Answer

Your sentence is correct, but the verb "encontrar" must be changed by "quedar". Susan y yo vamos a quedar con unos amigos para tomar un café. In this sentence you can't be "encontrar = see somebody by chance". 
The sentence of your partner is wrong, "nos" is making the same than "Susan y yo". You can say "Susan y yo vamos a..." or "Nos vamos a .." if the hearer knows you are with Susan. 
Finally "tomar un café" will be always correct but "tomar el café" is only correct if you usually have a coffe with they.
Sorry by my english level (you can correct me!)

Answer

I should traslate:  Susana y yo hemos quedado con unos amigos para tomar café

Answer

Está bien, solo que no es lo común.

Answer

Tu oración no tiene una estructura corecta, aunque si puedes usar vamos a en el siguiente caso:
SUsan y yo vamos a encontrarnos con unos amigos...

Answer

VERBO  ir junto a una preposicion  a,   indica movimiento por lo tanto se utiliza con un complemento indirecto y con unos amigos  no es complemento indirecto , se utilizaria ir a seguido de por

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