Have you ever used any alternative method of inserting data in to this database, such that you were able to confirm that the inserted data was not garbage?

If so, this means that you also have a means for pulling data out of this database in such a way that it can be displayed correctly as Chinese text (because otherwise, you wouldn't know whether or not the data was garbage).

And if all that is true, then it could be instructive to use your successful method of reading successful inserts, and get a hex dump of some successful output.

Then use that same method to read the garbage, again with a hex dump. This is likely to make it clear how the data are being transformed differently in the two cases, and might also make it clear what sort of pre-conditioning in your perl script (before sending the data to the server) would fix the problem. (There are several ways that things can go wrong, and it can be hard to tell them apart without a hex dump of both good and bad data.)