Steps to reproduce:
- go to Main.Welcome page (which has translations in almost all supported langauges)
- Add a tag, let's say "foo"
- On Main.Welcome, click on the tag to go to the tag page.
You will see that Main.Welcome is listed many times, because of the translations.
Note: Multilingual is set to NO, Supported languages has only en, and default language is en.
From a technical POV, it seems that $xwiki.tag.getDocumentsWithTag($tag)) does not return only unique pages.