Find a source that maps city names to timezone abbreviations and have the .tz command for Begiak (our IRC bot) scrape and use that data (e.g., ".time Barcelona"should give the current time in CET). You might want to model the scraper and storage after the .iso639 db scraper. For this task, you should fork the bot on github and send a pull request when you're done.
For further information and guidance on this task, you are encouraged to come to our IRC channel.