Nelson Mandela wasn’t talking about choosing between English, French and Spanish. What matters when you are trying to convince someone to do something is choosing your words so that connect to the other person’s experiences and emotions.

Giving clear instructions of how to do something will connect with a person’s intellect and transfer knowledge, but it won’t motivate him to actually follow those instructions.

Your kind words and actions may not always be returned in kind.  The other person may be in an exceptionally bad mood or may have experiences that make him distrust your real intent.  However, if you can manage to be consistently kind, that consistency will reduce the resistance to your approaches.  It is when our own feelings of anger and fear make it hardest to be kind that our kindness will have its most important impact.