Looked through the existing .po files.

german: Verwendung (patch corrects the erroneous display of "ung:")
french: Usage (like english; patch doesn't change anything visibly)
spanish: Uso, with additional spaces (patch wouldn't really hurt but increase indention of first line)
hungarian: Használat (patch corrects erroneous output)
italian: docstrings not translated
lithuanian: Naudojimas (patch corrects erroneous output)
russian: something as long as "Usage:" which can't be displayed correctly on my system ;-)
chinese simplified: something 3 unicode-characters long, no ':' (afaics)
chinese traditional: looks to me like chinese simplified

My patch would work for all languages (spanish could be enhanced by lstrip-ping blanks) *but* the two chinese versions. A universal approach could be to add a translation for "Usage: " and use its length.