Q:

How do I add timezone to date/time formatted by strftime?

I need to format date/time with a correct time zone and using this format string: %Y-%m-%dT%H:%M:%S. However, it's using local time. How can I make it format time including time zone, or using UTC time?

A:

You can add the timezone with %Z or %z.
strftime can only generate local time. 

