Asalamualaikum,
If I can just give my two cents on this discussion. I would highly recommend that you go through Ghamidi Sahb’s Tafseer on his website, specifically by looking at the verses where he uses “Haq Talafi” for ithm. There is a pattern in the context of these verses, which – in my view – shows that the term has been correctly translated by Ghamidi Sahb. All of these verses seem to concern situations in which another party is facing, or could potentially face, injustice. For example:
Qur’an 58:9:
O you who believe! When you hold secret counsel then (do) not hold secret counsel for SIN and aggression and disobedience (to) the Messenger, but hold secret counsel for righteousness and piety. And fear Allah, the One Who, to Him you will be gathered.
Qur’an 2:85:
Then you (are) those (who) kill yourselves and evict a party of you from their homes, you support one another against them in SIN and [the] transgression. And if they come to you (as) captives, you ransom them, while it (was) forbidden to you their eviction. So do you believe in part (of) the Book and disbelieve in part? Then what (should be the) recompense (for the one) who does that among you, except disgrace in the life (of) the world; and (on the) Day of [the] Resurrection they will be sent back to (the) most severe punishment? And not (is) Allah unaware of what you do.
Qur’an 2:182 (Read the two previous verses too):
But whoever fears from (the) testator (any) error or SIN, then reconciles between them, then (there is) no sin on him. Indeed, Allah (is) Oft-Forgiving, All-Merciful.
The translations are word for word by Dr. Shehnaz Shaikh, Ms. Kauser Katri, and more. I have bolded SIN where it is translated as “Haq Talafi” by Ghamidi Sahb in his tafseer.
There are quite a few other places where Ghamidi Sahb has translated the word ithm as “Haq Talafi”; however, I would have to take a look where I noted these instances down.
I think the pattern, whereby another party is facing, or could potentially face, injustice, is quite visible after reviewing these verses. Furthermore, it appears that Ghamidi Sabh and Islahi Sabh are not the only ones to have translated ithm in this manner. Orientalist scholar, George Sale, has translated ithm to a similar word – injustice – several times. For example:
Qur’an 4:20:
If ye be desirous to exchange a wife for another wife, and ye have already given one of them a talent; take not away any thing therefrom; Will ye take it by slandering her, and doing her manifest UNJUSTICE?
Qur’an 2:85:
Afterwards ye were they who slew one another, and turned several of your brethren out of their houses, mutually assisting each other against them with INJUSTICE and enmity; but if they come captives unto you, ye redeem them …
Qur’an 2:182:
Howbeit he who apprehendeth from the testator any mistake or INJUSTICE, and shall compose the matter between them, that shall be no crime in him, for God is gracious and merciful.
Qur’an 5:2:
Assist one another according to justice and piety, but assist not one another in INJUSTICE and malice: Therefore fear God; for God is severe in punishing.
Overall, I believe that a close look at the relevant verses shows that the translation of ithm as “Haq Talafi” is correct when the meaning is specified.
I hope that this helps and that I haven’t said anything wrong!
Some links to check out to double check:
https://www.javedahmedghamidi.org/#!/quran?chapter=58¶graph=6&type=Ghamidi
https://www.javedahmedghamidi.org/#!/quran?chapter=2¶graph=29&type=Ghamidi
https://www.javedahmedghamidi.org/#!/quran?chapter=2¶graph=84&type=Ghamidi