Some languages like sk in rP21907 have changed crucial line with information about how many plurals language uses and how to calculate correct one. However in plural_forms this line could not be matched with implemented functions so as result object with default settings have been returned what resulted in using only singular for translatePlural calls. (see https://code.wildfiregames.com/rP14951#inline-4907).
Affected languages (12):
sk, lt, uk, cs, pl, ro, mk, he, ga, cy, be, br
When no objections will raise, this will be committed in 3 days.