ui/gtk: fix gettext message's charset.

[yanminhui]

• set encoding of message translations is needed.

[crobinso]

Thanks for your contribution, but qemu doesn't accept patches via github pull request. Please close this request and instead send the changes to qemu-devel@nongnu.org

[yanminhui]

Thanks for your contribution, but qemu doesn't accept patches via github pull request. Please close this request and instead send the changes to qemu-devel@nongnu.org

Had sent.

[repo-lockdown]

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