English Wikisource has recently acquired a new namespace called "Translation" (namespace number 114) as a result of bug #50007.
We intend to transclude pages from the Page namespace (ns:104) into this Translation namespace (ns:114) with the ProofreadPage extension, as is already done in the Main namespace (ns:0).
In the main namespace, this creates a tab at the top called "Source" between the standard "Page" and "Discussion" tabs. The source tab links to the source master page in the Index namespace (ns:106).
However, in the Translation namespace, the source tab does not appear.
Example in the Translation namespace: http://en.wikisource.org/wiki/Translation:Daany_Beedxe
And the same transclusion in the main namespace: http://en.wikisource.org/wiki/Daany_Be%C3%A9dxe
I suspect something just needs to be updated with the 114 namespace number.
For reference, the effect of this change in the Translation namespace can be seen on this page (which includes a non-default dynamic page layout): http://en.wikisource.org/wiki/Translation:Sleeping_Beauty