You don't need to do ray tracing starting at the entrance and exit points. Think about what kind of light is hitting these points. A ray of light that hits the translucent surface at an angle other than the one that hits your target object will not affect the color of the light that does hit your target object.
+ * +
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+ * +
+ * +
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| +*+ |
| + * + |
| + * + |
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+ * +
*
*
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This assumes, of course, that there is no refraction in the material.
Now if you wanted to extend your ray tracer to something a little more advanced like path tracing, then you would need to consider the light that bounces off of the translucent object and hits your final object, but for a ray tracer you do not need do worry about it.
For the translucent object, I would model the decrease in light intensity as a linear function of distance (most real world objects adhere closely to this assumption). If you are modeling light as having RGB components (not physically realistic...) then you would decrease each component in proportion to that component's value within the object.
If you want to get really advanced with what the light does while in the object, then you will need to turn to subsurface scattering (the reason milk in a glass does not look like a white solid and why humans are so hard to model in CGI).
EDIT: The phenomenon you mention of light bouncing back and forth infinitely and using many calculations is what real light behaves like. Advanced renderers nowadays can't possible integrate all of these light components and so instead randomly samples light distributions. The more samples taken, the closer the image converges to looking realistic, and the closer the light integration becomes to its true value. This is called monte carlo rendering. Path tracing, bidirectional path tracing, and metropolis light transport are all monte carlo algorithms that attempt to simulate light transport fully. Each algorithm, given enough time, will converge to the same final image, however, some are more efficient that others. (See path tracing on Wikipedia. At the bottom of the article is an image better than the one I attempted to draw).