Hi @yuliab!
I took a look at choices.csv, and it looks like it contains a few non-ASCII characters: À, á, ã, ç, é, ê, í (perhaps others). Because of that, the file is encoded as UTF-8. (@yuliab, I think you have likely already seen this thread, but in case there are others for whom this odkmeta error is new, there was some discussion about it here.)
When I replace the non-ASCII characters with ASCII characters (for example, replacing À with A), I'm able to run odkmeta successfully. Once you have made those replacements, you may also need to save the CSV file so that it is not encoded as UTF-8. In my version of Excel, I used "Save As" to change the file format from "CSV UTF-8 (Comma delimited) (.csv)" to "Comma Separated Values (.csv)".
Hope that helps!