There are some ways you can stop lags in DF. One is press "Esc" and wait for 10 sec for the main menu to pop up. Go to "Settings" and change the graphics from Automatic to Good. If it still lags then change it to Very Low. That way the game won't lag as much.

Another way is to change Internet Browsers. The best Internet browsers are: Internet Explorer, Firefox, Google Chrome Maxathon and Safari.

Another way is to clear your internet cache with can e located in the Internet settings or history.(Depends on which browser you're using)

You can also download Ccleaner and clean out all the cache, history or other rubbish in your Internet browser.

There could be more ways but those are the basic ways to reduce lags while playing DF. If there is any other ways I found, I'll update this post.