Microsoft long ago added a mapping for 0x80 to the Euro sign to their CP936. While GBK 1.0 doesn't include this mapping, it is compatible, and Microsoft and glibc alias the two codepages. We could split them apart so GBK wouldn't include the mapping, but that seems like a lot of work for little gain.
aa4d00c localedata: GBK: add mapping for 0x80->Euro sign [BZ #20864]
localedata/ChangeLog | 5 +++++
localedata/charmaps/GBK | 7 +++++++
2 files changed, 12 insertions(+)
Upstream: sourceware.org