What is proper salutation to colleagues?

Answer 1

It depends on the professional culture. Some are more formal, and thus "Dr. Jones" would be most appropriate. Others are much less so, and either "Tom" or "Yo, dude" would be just as acceptable. Listen to what others are doing, and if in doubt, err on the side of politeness until invited otherwise. In a foreign language, use the formal address (Sie, usted, vous) until and unless invited to use the familiar forms.

In particular, be careful being too chummy with senior colleagues. They may say immediately, "Good heavens, don't call me Dr. Farnsworth, call me Hubert!" but let THEM extend the invitation to YOU!