Not sure if this will work, but try overriding the language of the in-text citation using the \l flag. Right-click on an in-text citation and choose "Edit Field...". In the dialog, there will be a string looking like " CITATION Bee69 \l 1033
". "Bee69" is the tag of the citation you are refering to, while "\l 1033" is the language used to display the citation in.
I'm not sure what influences the language of the numbers in the bibliography. I'm guessing the "lang" attribute plays a role here. You should experiment with that one. If I had the time, I would start by instead of assigning the same language to
the entire paragraph, by splitting the paragraph into two spans each with their own language attribute. So where you now have a
<p lang="xyz" dir="rtl" class="MsoBibliography">number text...</p>
you could try something along the lines of
<p class="MsoBibliography><span lang="abc" dir="rtl">number</span><span lang="xyz" dir="rtl">text...</span></p>
Of course dir would still remain dynamic depending on the language of your source.