Okay, this isn't exactly languages, isn't exactly trains, and isn't even exactly Brussels, but....

A possible short day trip would be to Antwerp. The fascinating Plantin-Moretus Museum, the site of a historic printworks, with the original presses and publications and a print collection, has a 16th-century polyglot Bible. The Central Station is an imposing, wildly eclectic late 19th century marvel, recently renovated and modified to add more levels to accommodate high-speed trains, including a multi-level escalator (on an incline, then straight, then on an incline). Antwerp has lots of other things to see and do, too.