I've been using TweetDeck to translate foreign language tweets, but TweetDeck requires two clicks per tweet to call Google Translate and translate the tweet. Do any Twitter clients, web based or otherwise, have this feature?
10+ Tools to Translate Tweets in Twitter Automatically lists a whole bunch of ways to do this.
Something you could try is to go to http://translate.google.com and put in the URL to your Twitter page, telling it detect the language. I admittedly, though, am not sure if it will do multiple languages from a single page...
The twitter search web interface has this functionality already:
Clicking this translates all tweets on the page to english, or presumably whatever language you have set in your preferences:
It doesn't seem to be be implemented anywhere else on twitter though, which is a shame, and I can't find any way of getting your timeline as a search query to use this. I do hope this is rolled out everywhere at some point
Use the Google Translate API. An example is in how to detect source language. Good luck!