The TGV from Barcelona to Paris is running, with two daily departures in May. Do note the reservation fee for this train is considerable (€35 to Paris on top of the pass).

Ah, thanks a lot. I don’t know how i got that mixed up.

can i just also ask, why can’t i seem to book any reservations on trains internally to Spain? There are a few i need to do, but it the website says i have to do it internally in Spain…

The Spanish rail operator RENFE have intentionally made it difficult for interrailers by blocking any method of booking reservations online. The only option for most is to book at Spanish rail stations. It is also possible to book through German operator DB but only in person at a ticket office.

That’s the policy of Renfe (Spanish national train operator). Making Pass holders it as difficult as possible to obtain reservations. Spain is a bit of an annoying country to Interrail through because of that.

The love between SNCF and RENFE is also over, since they are direct competitors now, on Spain’s domestic routes. So the two TGV’s Paris-Barcelona is the only proper international connection we will get this year unfortunately. 

The best thing to do, is to make all your reservations at once at a ticket office, as soon as you are in Spain.

There are other connections too, to France, but these do not go far over the border:

• Euskotren from San Sebastian to Hendaye (Fr), half hourly connection. In Hendaye you have good connection with trains to Dax, Pau, Bordeaux and Paris Montparnasse. Not in your pass, but Euskotren is very cheap. And probably your go to if you are in northwest Spain and want to travel to France without going over Barcelona.
• An infrequent local connection from Barcelona to Latour-de-Carol, with an okay connection to the nighttrain there to Paris or the TER to Toulouse. Quite scenic, this route! You also have Le Petit Train Jaune there (touristic railway in the Pyrenees), but only running in the high season I think.
• Local connection from Barcelona to Portbou(Es)/Cerbère(Fr) where you have connections to Perpignan and further.

Not as convenient alas these connections, but these alternatives can help you save you some money on the quite high reservation price of the TGV Barcelona-Paris.

Here and there was announced that RENFE itself=on its own account, would re-start the AVE trenes to Marseille and/or Toulouse later in the yr again. In fact there is quite a lot of unbelievable burocratic hassle to organise for that-and hitherto railways coöperated and simply let that be done by the one on the other side. 

But AS ESpana only had (and still mostly had) wide gauge and FR and the rest what is called normal there was always the need to change at border-and these connections as detailed above still exist-moreorless. As these also have no need for those pesky RES you are well advised to look into. But the todays pest is that these planners mostly only show fast/direct timings and that people also completely lack any knowledge of how trains work and run.

And-though for many it seems its even worse as cursing in church: you could simply also use a BUS (coach for GB) for short hops to cover those gaps. Could cost a lot less as a costly passday-and many on longer distance run also overnite-the wet dream of many a passholder old style.

Euskotren is indeed pretty useful if you’re in northwestern Spain: It takes about 40 minutes and costs €2.75 from San Sebastián to Hendaye, running every 30 minutes. From Hendaye it’s just 4h40 to Paris on a TGV.

The Train Jaune runs all year round and I really enjoyed it but it's not very useful (going via Cerbère to Perpignan is faster), not very frequent and very slow.

Not surprising: Renfe and SNCF stopped their cooperation, and the trains Madrid-Marseille and Barcelona-Lyon are indeed not running. Renfe hopes to have them running by the summer but it’s not yet entirely certain how this will go. It’s also not yet known whether passholders will be accepted.

Reservations in Spain are quite difficult to make, indeed. They can be made at ticket offices It's something Eurail is aware of, but for the time being they are indeed quite difficult to make.

As DB is able to make some of these too, there are also some DB travel agents that can make them. Seat 61 recommends one, for instance: “To make Spanish passholder reservations in advance, email andy@railtravelcentre.com, the same rail expert that runs www.discoverbyrail.com.  He can arrange passholder reservations in Spain, if necessary even at short-notice.  His normal handling fee is £17.50, but he'll reduce this to £12.50 if you quote 'seat61' in your email.  One handling fee is charged 'per booking', where a booking can be more than one passenger reserved on more than one train.  Remember to tell him if your pass is 1st or 2nd class.”

Alternatively, you can also order them from DB on the phone (I think their delivery fee is about €5.90), or collect them if passing through Germany. Or indeed book them on arrival in Spain. While up to the last seat is sold for passholders (contrary to for instance Eurostar), the trains can sell out particularly around weekends and in peak dates in Easter/Summer/Christmas/…

Thanks for all this amazing information everyone! As ever, the community on here are super helpful!