Add i18n support for mirror project

What does this MR do and why?

I was browsing the pages of JiHu GitLab and found that the mirror description of the detail page of a mirror Project was not been translated, so I added i18n support for mirror projects.

/cc @prajnamas

Screenshots or screen recordings

Page	Screenshot
Project show page
Project repository > commits page

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Numbered steps to set up and validate the change are strongly suggested.

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