Something appears to be wrong with these headers.
For example, in one case message proofreadpage_body is displayed in English ("Page body (to be transcluded)") regardless of interface language:
https://et.wikisource.org/wiki/?diff=58819&uselang=et
https://et.wikisource.org/wiki/?diff=58819&uselang=qqx
And in other case the same message is displayed in Estonian ("Tekstiosa (sisaldub)") regardless of interface language:
https://et.wikisource.org/wiki/?diff=42229&uselang=en
https://et.wikisource.org/wiki/?diff=42229&uselang=qqx