My workmates and I will go to have dinner.和I will have a dinner together with my colleagues 哪个更地道,更符合英美人表达习惯?

1.在美国职场习惯用 colleague 或 co-worker 来表达“同事”,一般小白领用后者,专业人士用前者多些.英国我不确定.
2.在口语对话时,都力求简洁,但语意必须表达清晰.
您的两句原文给我的“时间感”不同,所以无法掌握是“即将”去用晚餐呢还是“有计划”一起去用餐.
如果是立刻要去,下面两句都很地道,而且还可以继续接下文（如果不仅仅是为了通知别人的话）
My colleagues and I are going to dinner now ...
I'm going to dinner with my colleagues now...
如果是有计划一起晚餐,可以考虑下面这方式：
I'll be having dinner with my colleagues ...
My co-workers and I are planning to have dinner together ...
I will => I'll; I am=> I'm 在口语中都是用简略的