The aforementioned tags serve the same purpose across nearly all the languages and their wiki-excerpt mentions the following as well:
Date-difference will give difference in the number of days, months, years etc. between any two calendar dates. (synonyms in stackoverflow.com: datediff, date-diff, date-difference)
I'd request community to either burninate two of the tags (not voting for it) or synonimize the less used date-diff (13 questions) and date-difference (76 questions) and map it to widely used datediff (318 questions).