I have had the same issue in the past (how to produce files that Excel can read, and other tools can also read). I was using TSV rather than CSV, but the same problem with encodings came up.
I failed to find any way to get Excel to recognize UTF-8 automatically, and I was not willing/able to inflict on the consumers of the files complicated instructions how to open them. So I encoded them as UTF-16le (with a BOM) instead of UTF-8. Twice the size, but Excel can recognize the encoding. And they compress well, so the size rarely (but sadly not never) matters.
