Some languages need plural support for the count nouns. MediaWiki has patterns for the most of the languages and it is the only software I know which supports plural (and gender) fully. I am sure it is a pretty hard thing to do, at least for now.
pretty good solution has the GetText: Plurals defined as a math expression. E.g. Czech language has 3-4 plurals (1, 2-4, 5+, sometimes 0), defined like:
n==1?1:((n>1 && n<5)?2:(n==0?4:3))
1st form for n=1
2nd form for n=2..4
3rd form for n>=5
4th form for n=0
This seems to be a classic internationalization issue, not something related directly with how translate.uservoice is setup.
If the product was correctly internationalized, support for plurals would be already part of the strings.