Is it possible in google app engine (go) to format a date using the users local web browser timezone?
Ultimately users should be able to pick/adjust their timezone, but for now the users computer timezone should be sufficient.
You would need to send that information along the http request and then make sure is one of appengine's recognized timezones and then format it with the time package
you can read more about the whole thing here:
http://www.goinggo.net/2013/08/using-time-timezones-and-location-in-go.html
Depending on your application, but an appengine http request header should include few variables, namely 'X-AppEngine-Country' which is the country from which the request originated, as an ISO 3166-1 alpha-2 country code, determined from the client's IP address.
You may then able to use this country code (i.e. AU, GB) to detect the sender timezone and format the UTC time to local.
For user selected timezone, you would need to pass an information in as you may know.