In relation to ne deletion rates as

In relation to ne deletion rates as a barometer of the acquisition of
sociolinguistic speech norms, the effect of the year abroad is very striking.
The rates of ne deletion more than doubles after the year abroad, which
suggests that something important is happening in relation to the adoption
of native speaker community speech norms. It seems as if at this stage
the learner is sensitive to dialect issues in the second language. The speakers
become more non-standard due to contact with natives. They are
acquiring the grammar of the native speech community, so just as the
“normal” French person has a variable system, we have empirical evidence
of the second language learner also acquiring the details of variability, precisely
in the drive toward integration into the native speech community.
So the data shows that a period spent in the native speech community
affects the acquisition of sociolinguistic competence in an important way.
It also seems that this is affected by the amount of contact with native
speakers while abroad and that individual variation plays a role.