In the poem "Love Song for Lucinda," who is the speaker?

The speaker in “Love Song for Lucinda” is not identified. The speaker seems to be an enthralled but disillusioned lover, and probably a poet or poetry lover. In three stanzas, the speaker establishes a comparison with an appealing object or phenomenon, then cautions the reader about the possible associated ill effects. The speaker draws on earlier poems with the same objects but puts a different spin on them
In Stanza 1, like the taste of a ripe plum, the “enchantment” of love will never again be matched. This is an analogy to a classical Chinese poem, “Ripe plums are falling,” which appears in the Book of Songs.
The “bright star” of Stanza 2 evokes the title of John Keats’ poem about unwavering love; here the speaker warns that the light, shining into one’s eyes, will always hurt.
The third stanza cautions the reader not to climb too high on the mountain of love, lest they lose their breath. Several allusions are likely, such as Samuel Taylor Coleridge’s “Hymn before Sun-Rise, in the Vale of Chamouni” addressed to Mont Blanc, which calls the mountain “awful” and “dread,” or Friedrich Nietzsche’s “In High Mountains.”
https://www.britannica.com/topic/Shijing

https://www.poetryfoundation.org/poems/43988/hymn-before-sun-rise-in-the-vale-of-chamouni

https://www.poetryfoundation.org/poems/44468/bright-star-would-i-were-stedfast-as-thou-art

The speaker of the poem is presumably Hughes himself. Inspired by a woman named Lucinda, he wrote a metaphorical poem about love. In the first stanza, he poetically describes it as a “ripe plum growing on a purple tree.” With this comparison, he wishes to tell the reader that love is all of those magical clichés we see in the movies and read about in the books.
In the second stanza, Hughes describes love as a “bright star glowing in far Southern skies,” meaning it can be a very fulfilling and satisfying emotion, but it can also hurt you if you try to find logic in it, similarly to how your eyes will hurt if you look at the sun too closely.
In the third stanza, he compares love to a high mountain, explaining how it is only worth it if you’re willing to risk it. This is, essentially, the main theme of the poem.
https://www.poemhunter.com/best-poems/langston-hughes/love-song-for-lucinda/