Hi Xiaoyan -
Thank you for bringing this up – we have wanted to correct this for a long time but as Csaba and Andras have pointed out, it’s a big job and there are some very tricky parts (for instance making sure that files that mix text and numbers are correctly handled by some legacy C code). As you point out, providing guidelines for best practices for new code is a great way to start.
One of the biggest things we need to have is people who can test on non-US-English operating systems and data files. It would be great if you can share the work you have done, both the source code and any generated binaries so that we can all work together on this.
In case you hadn’t seen it here are some links to ongoing work:
https://na-mic.org/wiki/2011_Summer_Project_Week_Internationalization_of_Slicer
https://discourse.slicer.org/t/slicer-internationalization/579
Best,
Steve