That's so interesting. In Bulgarian we're starting to interchangeably use singular/plural versions of some of these words. E.g. "scissors" is "nozhici" (ножици), but very often used in its singular "nozhica"; similar with pants - nominally "pantaloni" (borrowed from French, of course), but very often encountered as a "pantalon". However, "pliers" and "glasses" cannot be comfortably made to assume a singular form, so they're always plural.