The Zombie Stack Exchanges That Just Won't Die
The language field (rft.language) is defined in The OpenURL Framework for Context-Sensitive.
If it is why Zotero could not retrieve language from COinS-based site that specify it with that field? To give an example, Zotero does not fetch language of following:
<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3aofi%2ffmt%3akev%3amtx%3ajournal&rfr_id=info%3asid%2focoins.info%3agenerator&rft.genre=article&rft.atitle=aa&rft.jtitle=bb&rft.title=aa&rft.language=fa"></span>
But can get language of following:
<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rfr_id=info%3Asid%2Focoins.info%3Agenerator&rft.title=a&rft.language=b"></span>
If you remove article from first it will be fetched. What is the solution? Also see following page that have this issue: http://www.noormags.com/view/fa/articlepage/495097
PHPst
Zotero does know about the language field in COinS. It implements
interpretation of COinS in the JavaScript file openurl.js
- this also
includes the language in
rft.language.
I guess there is something wrong with the COinS that you try import in
Zotero but not with Zotero.
Using @Jakob comment, Current Zotero OpenURL parser just fetch Language, description, subject ... fields if the item type defined as dc (Dublin Core). It seems that openurl.js should be modified.
see: https://github.com/zotero/zotero/blob/master/chrome/content/zotero/xpcom/openurl.js#L433
Zotero is merely following the OpenURL specification. The KEV format for info:ofi/fmt:kev:mtx:journal does not allow language, nor do the KEV formats for anything but info:ofi/fmt:kev:mtx:dc (Dublin Core).