Hello, the timetables are not up to date on the site and sometimes you have to make the routes and stages yourself.  I recommend a site like OBB, or even Ceske Drahy, two very complete sites.  Cheers

Hello,

there is just a connection with a change from Poland to Lithuania. This one you may find in the Planner app and reserve in Poland. 

Vilnius to Riga is not possible to do by train. Bus takes 4 hours.

From Riga to Talinn there's just one daily connection that takes 10 hours with local trains with a long change of 4 hours in between. You'd need to add this trip manually. (Going by bus takes just a little bit more for the whole trip than these 4 hours waiting time and is available from 12 €.)

Hello, 

But is the bus transportation, for exemple from Riga to Tallin, covered in the interrail plan? 

It is not.

That part of the world is not well-connected by rail. Come back in a decade or two when Rail Baltica is built from Warsaw to Helsinki!

The buses are not part of the pass.