B.Thanissaro sometimes leaves Dhamma untranslated, so why is

KN Iti 86 dhamm-ānu-dhamma-paṭipanna: proper practice

♦ 7. dhamm-ānu-dhamma-paṭipanna-suttaṃ (KN 4.86)	(thanissaro trans.)
♦ 86. vuttañhetaṃ bhagavatā, vuttamarahatāti me sutaṃ --	§86. This was said by the Blessed One, said by the Arahant, so I have heard:
♦ “dhamm-ānudhamma-paṭipannassa bhikkhuno ayam-anudhammo hoti veyyākaraṇāya —	“Monks, with reference to a monk who practices the Dhamma in accordance with the Dhamma,
dhamm-ānu-dhamma-paṭipannoyanti	it is this way of according with the Dhamma that he should be described as practicing the Dhamma in accordance with the Dhamma.
bhāsamāno dhammaññeva bhāsati no a-dhammaṃ,	When speaking, he speaks Dhamma and not non-Dhamma.
vitakkayamāno vā dhamma-vitakkaññeva vitakketi no a-dhamma-vitakkaṃ,	When thinking, he thinks about Dhamma and not about non-Dhamma.
tadubhayaṃ vā pana abhinivejjetvā	Avoiding both these things,
upekkhako viharati sato sampajāno”ti.	he stays equanimous, mindful, alert.”
etamatthaṃ bhagavā avoca. tatthetaṃ iti vuccati —	(then he said some more stuff)

(verse)

♦ “dhamm-ārāmo dhamma-rato,	Dhamma his dwelling, Dhamma his delight,
dhammaṃ anu-vicintayaṃ.	a monk pondering Dhamma,
♦ dhammaṃ anus-saraṃ bhikkhu,	calling Dhamma to mind,
sad-dhammā na parihāyati.	doesn’t fall away from true-Dhamma. --1--
♦ “caraṃ vā yadi vā tiṭṭhaṃ,	Whether walking, standing,
nisinno uda vā sayaṃ.	sitting, or lying down
♦ ajjhattaṃ samayaṃ cittaṃ,	–his mind inwardly restrained–
santi-mevādhi-gacchatī”ti.	he arrives right at peace.
♦ ayampi attho vutto bhagavatā,	(this was spoken (by) the-blessed-one,)
iti me sutanti. sattamaṃ.	(thus I heard.)

Note
1. This verse = Dhp 364.

So why does B. Thanissaro translate Dhamma vicaya-sambojjhanga  differently?

dhammaṃ anu-vicintayaṃ.

a monk pondering Dhamma,

from above, is the same as dhamma-vicaya-sambojjhanga  below "analysis of qualities"

SN 46.1

“There is the case where a monk develops mindfulness as a factor for awakening dependent on seclusion, dependent on dispassion, dependent on cessation, resulting in relinquishment. He develops analysis of qualities as a factor for awakening… persistence as a factor for awakening… rapture as a factor for awakening… calm as a factor for awakening… concentration as a factor for awakening… equanimity as a factor for awakening dependent on seclusion, dependent on dispassion, dependent on cessation, resulting in relinquishment. This is how a monk—in dependence on virtue, established on virtue, having developed & pursued the seven factors for awakening—attains to greatness & prosperity in terms of mental qualities.”

Dhamma-vicaya is ☸Dharma-investigation

Investigation of the Buddha's Dharma is what leads to viraga... nirvana.
Investigation of "qualities" leads to being a high quality person, high quality bank robber, high quality professional baseball pitcher, high quality of virtue that can lead to union with Brahma, joining Jesus in Heaven, any number of things that don't lead to nirvana.