First let's try to define what is meant by "language features." Usually this refers to diction and vocabulary, but, when used in reference to poets, it can take on the broader meaning of "poetic devices." Poetic devices include diction and vocabulary but also devices like metaphor, simile (a type of metaphor), imagery, symbolism, onomatopoeia, rhyme, and more, like irony and alliteration. We'll examine one or two language features to get you started.
I sit in the top of the wood, my eyes closed.
Inaction, no falsifying dream
Between my hooked head and hooked feet:
Or in sleep rehearse perfect kills and eat.
First of all, the poetic speaker in this poem is a personified hawk. When personification is applied to nature in this way, it is sometimes called "pathetic fallacy." Both terms are accurate while pathetic fallacy is more specific as it can only apply to personification of nature.
Since the poetic speaker is a hawk, the syntax of sentences (sentence structure) is simple, and the diction is not high poetic diction. Instead the diction is middle everyday conversational diction: "My feet are locked upon the rough bark." You'll note though that this is not a simplistic hawk even though his syntax is simple. Hughes has opted to endow this hawk with intelligence and a sophisticated vocabulary: e.g., falsifying, rehearse, convenience, buoyancy, inspection, revolve, sophistry, allotment.
Imagery that repeats is giving a sense of height: e.g., "top of the wood" "high trees" "earth's face upward for my inspection" "flight is direct." These are some of the most striking language features of this poem, yet these are not the only features. Knowing what is needed, you can analyze more of the language features like the descriptors used for the hawk itself (words used to describe the hawk) and the language that describes what the hawk does. You might also ask whether you find a metaphor in the description of what the hawk does.
What literary technique is used in the phrase: "...the earths face upward..." from the poem 'Hawk Roosting' by Ted Hughes?