Version 0.2
After a lot of time on the NewGraphicsSpecs site and a lot of decoded other grfs to understand the code (no, i didn't just copy the code from there

The Trolleybus Set replace the tram rail with Trolleybus overhead lines an has 11 trolleybuses. The buses and their Names are mostly based on some swiss trolleybuses, but aren't correspond to the original buses. the first bus is avaiable in 1920 and the last is instructed in 2019.
The Set works like a Tram set (because of the overhead lines), so you should use the trolleybus set with no other tram set. Otherwise, the trolleybuses drive on tram rails or the trams under the trolleybus overhead lines.
The set just use vehicle IDs which are defined here for trams. So it should be compitable with other road vehicle sets.
Unfortunately doesn't work the text string replacement in OpenTTD. But the set still works, the busses are just called "trams" instead of "trolleybus"

Have fun!