  Due to Multilingual Neural Machine Translation's (MNMT) capability of
zero-shot translation, many works have been carried out to fully exploit the
potential of MNMT in zero-shot translation. It is often hypothesized that
positional information may hinder the MNMT from outputting a robust encoded
representation for decoding. However, previous approaches treat all the
positional information equally and thus are unable to selectively remove
certain positional information. In sharp contrast, this paper investigates how
to learn to selectively preserve useful positional information.
  We describe the specific mechanism of positional information influencing MNMT
from the perspective of linguistics at the token level. We design a token-level
position disentangle module (TPDM) framework to disentangle positional
information at the token level based on the explanation. Our experiments
demonstrate that our framework improves zero-shot translation by a large margin
while reducing the performance loss in the supervised direction compared to
previous works.
