I know what you mean about always being proud of speaking well and clearly. I did too. It depends entirely on where and how much of your tongue is removed. And for a while after you have radiation, your sore mouth and throat plus the new loss of part of your tongue will really make you feel like you can't articulate at all. But possibly your partial removal will leave you with the ability to speak well after everything heals up, with little other intervention. Your ENT may give you mouth and tongue exercises to help strengthen them. You may be sent to a speech therapist to help get your speech back, as several on this board have been.
Hang in there, one thing at a time. Get the surgery over with and start to heal and reduce the pain from that. Then see the oncologists for a plan for radiation and maybe chemo. take all that a day at a time, and as you will read over and over from Christine, keep your nutrition up as much as possible. If you can even gain some weight between now and surgery, and then get some weight back on between surgery and radiation, do it. These couple of weeks are your chance to enjoy all the fattening foods that you're usually careful about!
Please keep us posted on your progress, I'm pretty new here but there are so many old posts that are really helpful, plus people with a lot of experience to answer anything they can for you.
It's not a fun journey, but you'll get through it, and I'll sure be wishing you the best as will everyone else here.