The following options may be helpful for avoiding overuse of specific noun-adjective pairs:
Replace the noun with another noun which has a similar relationship to the adjective. This is the simplest and most obvious method. In place of "jet-black" you could, e.g., use "coal-black" (I actually had to look up the definition of "jet" and learned it was lignite [coal]!), "soot-black", or "obsidian-black". This simple solution has at least two issues:
- If one is overusing one noun-adjective pair, diversifying the noun-adjective pairs will probably still keep the problem of excessive use of noun-adjective pairs and might introduce a feeling of trying too hard, of artificial replacement, because the phrasings are too similar.
- The original noun may have intentionally associated a connotation or play on words (e.g., "jet-black eyes" which later "burn with rage" or a "pitch-black night" where oppressive humidity seems to make the night air stick to the skin) which would be removed or the replacement noun may introduce unintended connotations (e.g., "he looked into the princess' beautiful soot-black eyes"—even for a Cinderella figure that is likely inappropriate).
Remove the noun. If there is enough description earlier or nearby (yes, the description can be placed shortly after the adjective), the simple adjective would act something like a pronoun, simplifying the phrasing and recalling the antecedent to the reader's mind. E.g., "His pitch-black eyes stared at her, and she shivered at their cold darkness" might be replaced with "His dark eyes stared at her, and she shivered at their cold blackness" (yes, this also swaps the "dark" and "black"; but I think you get the idea).
- This method may be particularly appropriate when the portion being written is already very dense with description, even when the description is not directly connected with the simplified part of the text. (Extensive description can give a feeling of opulence or oppressiveness, or hint of the narrator's unusually intense observation ['excess' of description intensifying some 'excess' in the story], but usually moderation is appropriate.)
- However, the intensifying effect of the noun may have been sufficiently significant to the scene that trimming other description would be more desirable. This method is also limited to cases where some trimming of description seems appropriate (and sometimes in that context simplicity adds its own emphasis) or the description is somewhat redundant. (Note that even something as simple as an earlier description of a family member with "jet-black eyes" could provide a sufficient antecedent to allow the use of a simple adjective.)
Use a simile. While this allows the retention of the specific descriptive noun (with all of its connotations), it increases length, it can introduce awkward phrasing, and it can otherwise interfere with the pace or feeling of the writing. E.g., "his pitch-black eyes swept over the prisoners without pity. 'Kill them all.'" seems to have better pacing than "his eyes, black as pitch, swept over the prisoners without pity. 'Kill them all.'" and "his pitch-black eyes showed no pity" avoids the potentially 'upbeat' alliteration of "his eyes, black as pitch, showed no pity".
Remove the adjective. While acceptable in English, replacing a noun-adjective pair with just the noun—or an alternative noun—must be done with significant care. E.g., in some cases "obsidian-black eyes" could be replaced by "obsidian eyes".
- Confusion between 'made of' and 'having the properties of' is a significant danger in some cases. E.g., in a fantasy where stone might be enchanted, "the mage's obsidian eyes stared blankly at his bumbling apprentice" might be quite ambiguous.
- Uncertainty about which property is implied can confuse the reader, breaking the flow of the text.
- Sometimes the feeling is the primary concern and matches well, e.g., "obsidian-black eyes" and "obsidian eyes" might both communicate an unnatural, inorganic, dark feeling which may have been the primary intent. Sacrificing some literal specificity may be acceptable in such cases.
- Rarely all of the properties that are consistent with the context and typically associated with the noun apply. E.g., replacing "obsidian-black eyes" with "obsidian eyes" could communicate not only the blackness but also perhaps a hardness and coldness which are only later explicitly or implicitly shown to apply.
Replace the adjective with a more generic adjective. E.g., replacing "jet-black hair" with "jet-colored hair" might be acceptable in some cases.
- This typically reduces the intensity of the description, though perhaps not as much as simply stripping the noun.
- There is not always an appropriate more generic adjective.
- As with using a different noun, this will not reduce any overuse of noun-adjective pairs.
Use a more intense or more specific adjective. A more explicit adjective can reduce the need for additional intensification or specification. E.g., replacing "pitch-black night" with "starless night" may fit the setting, the mood, and the meaning.
- Often some specificity or intensity would be sacrificed by such a change, so such is generally more appropriate when the lost sense is less significant to the scene or the sense is already shored up somewhat by the context.
- The adjective in question may not have an appropriate alternative.
Use an adverb with an adjective. While a noun-adjective pair provides a concrete specification to intensify the adjective, using an adverb can sometimes be a reasonable substitution. (I cannot think of any good examples—e.g., rather than changing "rock-solid trust" to "unbreakably firm trust", using "unbreakable trust" makes more sense!)
Use a companion adjective. In some cases, a second adjective can be used to add relatively little new meaning while substantially reinforcing the intended connotation. E.g., replacing "her jet-black eyes" with "her soft, black eyes" (the comforting darkness of a peaceful night and jet is a soft and organic stone), "her lovely black eyes" (jet as a semiprecious gem), or "her deep, black eyes" (deep is a weak intensifier in this case) might communicate most of the intention of the author.
Substantially rephrase the scene to distribute the desired feeling and meaning over a larger portion of the text. This may be the least desirable of the alternatives. Not only will such tend to be more work simply from expanding the scope of the change, but keeping such scattered changes from damaging other parts of the text can be very difficult.
Even though you are working on translations, I am going to boldly present reworkings of the snippets you provided rather than simply answering your question about alternative wording. Although you can freely use any of the changes, I suspect that they (and their rationales) will be more useful as general assistance than as specific suggestions, especially within the context of translation.
As I watched him walk out of the arrivals gate and look around the airport, the first thing that sprang to mind was the crazed passion that struck me a decade ago and the boundless darkness that lurked on the two mountains. The dense forest, stained black by pine resin, set the backdrop along with the tilting house I peered at every night.
(It was unclear whether the last sentence was meant to say that only the house set the backdrop or if both the forest and the house set the backdrop; a comma with "and" usually separates clauses not mere phrases but without "was" added to "stained" the first part would not be a clause. I am guessing that both are intended to be part of the backdrop.)
- reversing the order of "as ... airport" and "the first ... mind" brings the intense action verb (sprang) close to its 'subject'
- replacing "crazy fervor" with "crazed passion" seems a little more intense (one less syllable) and might better fit the intended meaning
- "on the two mountains": in this context, "in" would seem to have the sense of "among", which seems less appropriate for two objects; "on" also has a little bit of an overshadowing feel which seems to fit the context
- making the forest the subject of "set the backdrop": this change emphasizes the forest (quite possibly too much) over the house, but strengthens the sentence by moving the verb closer to the beginning
- removing "jet-": enough description might be provided by "stained" and "by pine resin" (it might be appropriate to add something like "aged" to "pine resin" since fresh pine resin is nearer a golden color; "aged" might incidentally add to the sense of gloom) and the abruptness of "stained black" seems to have a harder feel than "stained [intensifier]-black" (flowery language—even if only in the sense of richly descriptive—tends to work against a sense of gloom)
- replacing "and" with "along with" allowed the "house" clause to be moved to the end of the sentence, increasing the emphasis on the 'dark word' "night" (it is also possible that sidelining the house might slightly intensify the feeling associated with "tilting"—off-center, to-the-side); even so, this also seems a problematic phrasing
For a moment I stopped speaking. At every turn of the story flowing from my mouth my mind had hearkened back to the village, and I recalled that starless night when I realized that as long as he existed, I'd never amount to anything more than third-rate.
- reversal of "for a moment" and "I ... speaking": this seems a doubtful change but it moves the stopping closer to the next sentence, connecting the break in speech with the thoughts that interrupted the speech, the end-of-sentence emphasis is on "stopped speaking" rather than the momentary nature of the pause, and stopping is linked with a full stop mark.
- reversal of "at every ... mouth" and "my mind ... village": rather doubtful suggestion (particularly since if a comma is added after "mouth" it will weaken the break at ", and I recalled"), but moving the remembering of the village closer to the recalling of the night has some value
- "had hearkened back": since this is a deeper past event than the "stopped speaking" using "had hearkened" seems more appropriate ("returned" might replace "hearkened back" if a casual feel is desired, but "hearkened" seems to have an appropriate nostalgic, possibly 'backwoodsy', feel)
- replacing ". I also" with ", and I" improves the flow (it was only a momentary pause in speech)
- replacing "one" with "that": "that" refers to a specific night
- replacing "pitch-black" with "starless" touches on the actual content of the question, "starless" implies a very dark night (and incidentally gives some feel of hopelessness, stars being associated with wishes, dreams, aspirations)
- replacing "it dawned on me" with "I realized": this removes what I am guessing is an unintended play on words ("night"/"dawn"), slightly tightens the phrasing (three vs. four syllables and active voice vs. passive), and (perhaps wrongly?) replaces the slightly positive and sentimental(?) connotation of "dawned" with a slightly harsh, rational, and realistic connotation
- replacing "I wouldn't ever" with "I'd never" tends to keep the informal tone (though less 'backwoodsy') and increases the intensity
He did not reply. His unsearchable black eyes frightened me [or "were frightening"].
- replacing "impossible to read" with "unsearchable" may intensify the feeling and imply that intently looking at the eyes was impossible not just discovering their secrets being impossible
- applying "unsearchable" to "black eyes" and not just to "eyes" (i.e., not "unsearchable, black eyes") intensifies the blackness and associates the eyes' unsearchable nature with the blackness
- replacing "were scary" with "frightened me" would be more direct—"scary" also seems to have a slightly juvenile, less serious tone ("terrified" might be too intense)—but "were frightening" might well be more appropriate (e.g., if it was not just the narrator who was frightened or more emphasis is desired for their general terror, i.e., they would frighten anyone)
How could I not be afraid of the night, shrouding the world in front of me in its impenetrable darkness?
- replacing "fearful" with "afraid": very weak suggestion, it just seems 'better'
- replacing "that was" with ", ": increases the pace of the sentence and more tightly binds "shrouding" with "night"
- adding "its": associates the darkness more tightly with the night and gives a more involved, almost personal feeling (e.g., compare "he stabbed it with a knife" and "he stabbed it with his knife") which seems to deepen the terror
- replacing "pitch-black" with "impenetrable": another answer for the actual question, "impenetrable" has the same effective meaning—so dark one cannot see—but enhances the feeling of helplessness and isolation