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The viewpoint character is an American non-violent pacifist and his antagonist is a Russian lady linguist who knows the language of the natives, but has nothing useful to tell them. The natives fly through the dense atmosphere of this planet.

"Something to Say", a novelette by John Berryman, also the (unaccepted) answer to this other question; published in Analog Science Fiction -> Science Fact, August 1966, reprinted in the 1968 anthology Analog 6 edited by John W. Campbell.

The viewpoint character is an American non-violent pacifist

I shrugged again. "I'm neutral," I said. "If that means anything. But you know I'm not going to put up a fight if some bandits come after my vehicle with lasguns."

"That is a hitch," he agreed. "I know you have the right, as a Non-violent Pacifist, to refuse to carry a sidearm, but I hoped you wouldn't insist on it."

I had to shake my head. "I'm sorry, Chief. I am committed to non-violence."

and his antagonist is a Russian lady linguist who knows the language of the natives,

I laughed, backing away from her aggressive advance across the stone floor. A little common sense started percolating through my thick head. Our interests were adverse. She had landed on Six to grease the way for the Sovbloc, in violation of the Interplanetary Treaty. The mission I was part of on Six Beta had been recruited to prevent either Bloc from getting a preferred position.

"You want to know too much," I said, continuing to chuckle. "It's time I clammed up."

She shrugged, ramming her fists onto her hips, her feet apart. "You won't talk, eh? So I'll ask them." She sounded pretty smug.

I let defeat sound in my voice. "You mean you can talk with them already?" I wanted to know.

"Hah!" She leaned back to throw her words at me. "As if I should answer your questions! Well, there is no reason why not: Perhaps I can't exactly talk with the natives yet. But I have identified ten or twelve operators in their speech."

"Operators?" (Hollowly.)

"Oh, you know," she said with that viciousness which is peculiarly feminine. "The really important words. 'Through.' 'By.' 'Between.' 'Under.' 'Because.' That kind."

"Oh." (Grudging respect!)

She laughed softly, letting her hands fall to her sides and moving slowly toward me. "You would have been trying to identify nouns, I suppose, Mr. Reamy?" she asked lazily.

"Maybe," I agreed doubtfully. "I couldn't operate the way you are going about it, that's a cinch."

"The advantage of being a trained linguist," Diane told me. "And just to cheer you a little, L. C. Reamy, you might as well know that Sixian is a positional speech, like Chinese. But unlike Chinese, it is inflected about as much as Sanskrit."

but has nothing useful to tell them.

The chief shook his head. "I can't understand it," he said to her. "Here you are, a prize linguist, able to talk a blue streak with the locals. And here's Reamy, making dumb-show with his hands. How does it occur that he has them in the palm of his hand, and you are still a captive?"

She shook her head. "I should have killed him when I had the chance!" she said.

"And you can't tell me how he did it?"

"No, I can't," she said angrily.

The chief turned back to me.

"She overlooked one thing," I grinned at him. "You have to have something to say."

The natives fly through the dense atmosphere of this planet.

"This is one tremendously deep atmosphere. At the surface, pressures are almost six times standard. But the oxygen percentage is only one sixth of standard."

[. . . .]

There was a pilot in each of the soaring things, sitting, lying, or standing, I had no way of knowing, in an open cockpit. He was steering his glider with what appeared to be two hands, and his upper end—if that's what we were looking at—was shockingly human.

Bird-like, or airplane-like, the stubby-winged gliders made a series of rough, slipping turns in a pattern and prepared to land single-file forty or fifty meters from where we sat in the bracken. As they flared out "over the fence" they wobbled in near-stalls, accentuated by the extremely low aspect ratio of their wings. At the comical last moment, the "landing gear" was extended. Just two of the most human-looking legs and feet you ever saw. Each pilot trotted a few steps and squatted down, grounding his glider.