Is it possible to turn on subtitles in bonus contents ?

Cireka's Vow is spoken in Githyanki, and subs doesn't work... another strange thing is that in the console version of the game, Cireka has automatic subtitles when she speak, even if them are deactivated, BUT in the GOG version if subtitles are off, you can't understand what she says !! (at least if you don't know Githyanki language...)

EDIT: I found a guide with a translation

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---- SPOILER ----
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Prologue: Cireka's Vow (translated from Githyanki).
"I am Cireka, High Clanswoman of the Kith clan, General of the Guard of
the First City Tu'narath. Lord of the Qual'kith, Conquerer of the Lingering
Lands, and daughter of Na'kulith, daughter of Vlakith, she who watches over us
all. The path of the righteous is often bathed in the blood of lesser species
such as yourselves. But your minds cannot hold the glory that we Githyanki
have seen. The glory of perfection. Your lands will be conquered, your cities
occupied. and in their place, there will be order and there will be peace.
The ends always justify the means, and for this goal, there is no method beyond
our consideration. I am better than you. I am stronger. I am wiser. My mind
can hold such visions that would crush your pitiful skulls. I am your enemy
because you cannot see the clarity that I can see. If you were to have an
inkling of that vision, your race would surrender to us immediately. Some of
your kind will no doubt serve in this glorious order. It will be an honor for
you to serve us in our grand expansion, though none of you will be wise enough
to cherish the role you must play. When Faerun is conquered, and I have
delivered your species as slaves, it will be my great honor to sacrifice myself
to Vlakith, enriching her, and all my people."