QGIS » QGIS Application

Tried on QGIS 2.18.23 and the encoding is properly manage. It seems it is indeed a QGIS 3.X.X problem.

first rough test on a shape with changed encoding to korean, generate the result in the correct encoding... now checking the attached shape that is originally generated with a no UTF8 encoding. BTW just for not, please use data subsets instead of a big example data.

This is not a bug but a feature ;). the standard temporary format in qgis processing is always gpkg, that by default has only allowed UTF-8, UTF-16BE or UTF16LE encoding.
In fact if you select a no-temporary file as shapefile, the output respect the encoding because the format allow you.

IMHO this is not a clear bug. Can be solved adding a validation before to run any grass command that involve temporary file where the original source is not UTF8 or UTF16.

I'll investigate if it is simple to add this check, but probably have to be discussed if have to be implemented or not.

I'm not sure what would be a decent solution. A generic use case would collect provider encoding for all inputs, then check if there is an out in gpkg (or some other format with limited encoding) and check if input can be mapped in output encoding.
Because the nature of processing, any check should be related to the nature of the grass command to map correctly if input encoding is propagated to an output layer.
IMHO there is no a generic solution and any generic solution does not consider the nature of the grass command with the risk to create false alerts when not necessary.
The possible workaround is to better document the correct use of the backends. e.g.
If you use temporary file they will be gpkg (if configured) and then UTF8/16 encoded. If your input data use different encoding take care of:
1) do no t use system but prefer explicit and correct encoding
2) take care that this encoding will be changed to UTF8/16 if you use temporary gpkg out files

Bastien Ferland what do you mind about my comments?

I red your comments and now I think I understand the problem. Saving as temporary files will always create a UTF file (because it's a gpkg) meaning that I have two options: 1) convert my source file to UTF before the grass command, or 2) don't use temporary file and save it directly in a specified file. Do I understand properly?

Adding a warning would have been nice, but if it's not possible, I agree that adding a note in the documentation for temporary file is acceptable. That, plus this thread, should allow people to fix the problem quickly when encounter.

Thanks for your time.