A causal connection between certain actions and certain outcomes may be identified. Such a connection is then tested when the planned actions are carried out. In fact, as action research is intended to produce action, this is usually an emphasis. In that sense, causal understanding actively pursued. Yes, though it is usually qualitative.
People communicate naturally in language.
Communication is an important part of action research, especially in its more participative varieties. Quantitative measures can be valuable. But developing them requires a substantial investment in time. This may not be warranted if you are likely to change your mind about the measures that you need. When suitable quantitative measures are available, there is no reason why they may not be used.