Could be... D3D9Client (at least the 2016 Version) is not build for wide-character sets, so that might be an issue. But as the Orbiter API also is 8-bit characters it would be a big impact to change it...
And it would be almost impossible for me to test

To get to the root-cause, maybe the OP could try and change
only the decimal-separator. If that fixes the issue, we at least know that this alone is the culprit.
If not...I think there's not much I can do about it, as debugging is almost impossible without having a "Traditional Chinese" System.