RE: specifying fonts when latin and complex scripts are mixed together.

I have cases where latin characters are intermixed with complex script
characters e.g.:

2015年12月

Here the 2015 needs to be "Arial" and the Chinese script in "SimSun". This
is a chinese language document. Is there a way I can tell the xsl-fo
processor to use Arial for latin characters when they appear within some
blocks ?

Right now it uses SimSun to render 2015 and 12.  I also have cases where
Abbreviations are in english (to be rendered in Times Roman) followed by
chinese characters (SimSun).

Ashok