Dates should be presented in the language, the format, and the timezone the user should configure in his/her user configuration.
Some users even using the same language don't like the default date/time for that language. Some Americans like the 24-hour format and some people like ISO dates (YYYY-MM-DD)
Some people also like to see date/times in the local timezone and not just UTC.
If the user haven't entered this configuration somewhere you should display dates in ISO date/time format and UTC
