Don't worry, especially in Kaiserslautern area (American air base nearby), most people under 40 will probably speak pretty good English. Just start with "Sprechen Sie English?" and it should not be a problem.
As you might have gathered, Germany has an excellent train system, with buses, often coordinated with the trains, providing "last mile" service. So if you used the link Gary Mc provided, you'll see there is a train once per hour that will connect you to Kaiserslautern via Mannheim and 7 minutes later there will be a bus No 140 to take you to Weilerbach. Every bus I've been on in Germany, the driver takes cash, unless you try to use a 50 EUR note for a 2 EUR fare.
Oh and the start station at the airport will be Frankfurt(Main) Flugh. The website is very good at suggesting possible stations you are looking for, but since there are towns named Weilerbach and Weilersbach, it will not know which one you want.
Click on the details to see each connecting point and a box below "station information" will give you all the hours and services at the station, local street map, and for larger stations, a station map. And the "map" link next to it will show the route in a map of Germany.