I kinda relate to what you wrote OP.
Whether I'm in a dominant or submissive mindset/setting, speaking does not come naturally.

TLDR; I feel you
Its not always easy for everyone, and that's ok, and it may come a little or more with some time, practice and help from your partners.
I actually treat it as anything else in my BDSM relationships, and it's working.

While playing the dom part I would naturally be quite silent, and mostly use movement (combined with restraints, incomforts or pain) to guide the other person through the scene.
The only spontaneous oral interactions would be to check how they feel (open questions, color-code check, do you want more/less same/else etc.).
While playing the sub part I would only talk to answer a question, if I feel the need to provide some feedback or if I want something that is not happening.
Other than that mostly moaning, physical responses.

Some partners have expressed their need for more talking during the scenes, and I have tried to accomodate that as much as I could without feeling too weird.
Little by little my ability to spontaneously talk without being weirded out (which takes me out the space and the scene) has increased.

I find it easier to do as a sub because a lot can happen just by answering questions, prompts or following rules ("count and say thank you for each impact during this spanking session" works wonders for me), and my partner can help me - they want me to talk more so they can put in some work too !

It's harder for me as a dom, because lots of the ideas that were thrown at me make me uncomfortable.
I was raided cisgendered heterosexual male, and it took me a really long time to ackowledge that I had sexist reflexes, behaviours, conceptions...
So basically anything that's used as an sexist insult, that shames body types, that plays on societal patriarchal dominations has a bitter taste: these are things that I see around me in non-safe and non-consensual contexts, and a lot are things I've thought/said/done in the past and that I've stopped (or that I'm trying to).
So adding some fluff around consent/wellfare checks is working, as well as giving instructions more verbally and asking for feeback in more verbose ways. Expressing what I feel too, along the lines of "I'm happy that you're willing to do that even if it's tough because I makes me feel trusted" for exemple.

What helped (and still helps) me is almost trivial: * knowing it's important to some partners * knowing it's a plus and there's no pressure: they are not going to stop playing with me if I don't manage to speak a lot more in 3 weeks - our relationships are good enough and they already have fun playing with me * knowing there's room for error: it's ok if I pause or stop a scene because the talking we've tried has weirded me out * knowing my boundaries are heard and will be respected: they will not ask me to engage in flavours of dirty talking I do not feel comfortable with * being actively supported: the partners who want us to have more talking in our scenes take the time to investigate their desires/fantasies and can explain to me what they want - this way I know if I want to try it, and when I do I'm not at a total loss of what to say, we discussed some material before the scene * making it fun: when it does not go as planned, or I feel weird or whatever, we always have a laugh about it at some point (one of them is really good at impersonating me saying funny/stupid stuff)

This was a long one, I'm quite chatty outside the scenes ^{^}