Check out the inflect package. It will pluralize things, as well as do a whole host of other linguistic trickery. There are too many situations to special-case these yourself!
From the docs at the link above:
import inflect
p = inflect.engine()
# UNCONDITIONALLY FORM THE PLURAL
print("The plural of ", word, " is ", p.plural(word))
# CONDITIONALLY FORM THE PLURAL
print("I saw", cat_count, p.plural("cat", cat_count))
For your specific example:
{print(str(count) + " " + p.pluralize(string, count)) for string, count in data.items() }