I have years of experience maintaining an application where I did use plural forms in some strings. The problem is plural forms are evil! :) Even though I dutifully went through the gettext manual and learned about how to implement plural forms in the software - I lost count of how many translators did not understand how it's supposed to work and either didn't translate those strings at all or translated them wrong, not using the plural system correctly.
The OSTD services will try and work with po/pot files that have plural strings without failing completely, but it's unlikely that I'm going to implement plural form support as a working feature. Sorry if this is inconvenient.