To a certain extent, there may be a tendency to commit direct translation in terms of using mother tongue knowledge when learning the second language. This will result in negative acquisition of the second language. Learners need to be made aware of the dangers of allowing mother tongue influence when learning a second language especially when learning grammar as rules vary.
Indubitably, previous learning habits can affect one's subsequent learning. The concept of transferability has had a long history and has been received with positive and negative reactions. Depending on the direction of learning, transferability may be either beneficial or detrimental. For instance, for teaching L2 grammar, cross-checking of L1 grammar rules with those of L2 can be pedagogically useful. However, for teaching L2 speaking skill it is not very practical. In point of fact, a teaching context involves quite a wide range of variables which may or may not necessitate the use of L1 explanations . Besides, the decisions adopted much depends on the teacher's discretion in adopting one particular strategy rather than the other.
Interaction of the two systems is complex. However, it is clear that the more proficient you get in your second language the less you are influenced by the linguistic system of your first language.