Full Idea
Historically the problem of universals has mainly been about the "One over Many", which involves giving an account of the unity of natural classes.
Gist of Idea
The traditional problem of universals centres on the "One over Many", which is the unity of natural classes
Source
J.P. Moreland (Universals [2001], Ch.1)
Book Reference
Moreland,J.P.: 'Universals' [Acumen 2001], p.1
A Reaction
This still strikes me as the main problem (rather than issues of language). If universals are not natural, they must be analysed as properties, which break down into causation, which is seen as a human convention.