Ah well, it's good he had 2 improved nights
And you are always welcome to share your woes here!
So, here's what I was going to suggest.
In the short term, to help you get through the phase, give a long nap and suck up the 9hr nights (because he is not doing longer regardless) so something like:
WU 6
nap 12 - 2
BT 9 (or 8pm if nights are getting longer)
which I realise doesn't look good but gives a steady 11hr sleep in 24 (might lengthen after the language leap) and might help his mood. It covers the given stipulations which from memory were 6 hrs A to nap, 6-8 A to BT.
I do think it's a phase but even phases need a way to cope. My thinking is that if you give the nap too early he ends up with far too long a day, OT by BT which may not help with the EW.
I would try again with set nap and BT as closely as you can (moving BT earlier if nights are lengthening in general rather than a one off) so he has a chance to regulate his sleep and knows when the S times are coming.
FWIW our journey towards nap drop involved 9hr nights, which was when I started altering his routine to accommodate. As it turned out mine could not cope with capped naps, nor with one off no nap days, so the long nap and short night continued for a while (the night actually lengthened a little again) until he totally dropped the nap, overnight.
Nights (and overall sleep in 24hr) did not lengthen until he had totally dropped the nap and settled into the routine. After settling we got 12hr nights which is more sleep in 24hr than with nap plus night. This is quite common.
It does sound like your LO may be moving towards dropping the nap even if this current disruption in a phase of language development etc so maybe keep that in mind over the coming weeks/months if things do not improve.
You may need to look at capping the nap or offering some no nap days to maintain night sleep - or accept shorter night and a well rested toddler - until he can cope with a full nap drop.
We'd be very happy to support you during the transition - even if just to offer hugs and a place for you to off load the frustrations.