Your students can get plenty of English practice by speaking English with their teachers on campus, and, more importantly, with each other. You need to create an English speaking environment where the official language of your department is English, where practicable. Listening, reading, speaking & writing more English is the only way to prompt their mental lexicon. This is the only way you can get a noticeable improvement from your students.

NEVER invite a foreign teacher to "chat" with your students. We are not here to be used as test subjects in a useless experiment. Let me give an example:

10 classes of 40 students have 2 "Wai Jiao" periods a week.
So each class has 90 minutes a week.
Compensating for minimal teacher talking time, each student talks to the foreign teacher for 2 minutes a week.
There are 32 weeks in the academic year; so
The student gets to talk to the foreign teachers for 64 minutes a year, and that is assuming the foreign teacher even cares, as he was not given any training, structured goals, or teaching materials. You probably won't even give the course he teaches a proper name.

Please give consideration to the above,

Thanks.

Extc