From http://bugs.debian.org/531562. please qask the submitter directly when you
have more questions about this.

--- snip ---
I find it misleading that I don't get informed whenever a font is 
substituted e.g. in a Writer document. Don't get me wrong, I believe 
font substitution is a valuable feature and I have it enabled 
knowingly, but sometimes it leads to unexpected behaviour.

For example, there is a document available on [1] that aims to compare 
the metrics of some freely available fonts with the ones from Times 
New Roman and Arial. If I have neither of these fonts installed on my 
system but only e.g. ttf-dejavu, then *all* fonts in this document 
will look the same on my computer since they all get substituted with 
the dejavu fonts. So all available text in this document will look the 
same, because it is rendered in the same font. However, when I 
highlight some text, the font chooser box still tells me that the 
current text is written in e.g. "Times New Roman". This isn't wrong 
either, since the text is formatted in TNR, but it doesn't tell me 
that what I see is actually not TNR, but dejavu-serif.

So what I'd like to see is some visible hint that tells me font A has 
been substituted by font B on my system, because font A could not be 
found.
--- snip ---