Translatord differ in how they translate based on several things, from personal preference to wording, or grammar, to there take on the validity of the commentaries, or philosophical understanding of the teachings, or there preference in regard to the philosophical model they use to understand the teachings, but do these translations really say anything different?
essentially no, they are saying "this is the way this reference is so contemplate it as such"!
I translate this line in two different ways
Idha, bhikkhave, bhikkhu kāye kāyānupassī viharati,
“Mendicants, in this existence, ‘a meditator abides contemplating the body as just a body,
Iti ajjhattaṃ vā kāye kāyānupassī viharati,
You should also abide contemplating the body as a collection of parts regarding yourselves (internally,) or
and my footnote to the first
An alternative translation of ‘kāye kāyānupassī viharati, etc.,’ maybe ‘abide contemplating the body in the body, etc.,’ which indicates that it is only, the specific reference being used that is the object, not another reference such as feelings, mental qualities, or mental phenomena. However, both translations indicate that it is just reference being referenced, not a male, female, ones own body… rather simply what it is, as it is.
A third alternative is given within the text, which I believe to be in-keeping with the 'insight' aspect, rather than the 'tranquillity' aspect reflected here.
The second translation is from the insight refrain within the body section and the first from the introduction, and both are essentially saying the same thing just the emphasis on the style of practice has changed because the actual section is obviously referring to a development of insight rather than the stock phrase of the introduction which could be used as a basis of practice for either but I felt having a more tranquillity slant more appropriate, as the phrase implies more to me this in the context, but this is just my personal interpretation, not that of the vast majority in regard to phraseology.
The words are known well enough and to some extent known through existing use within language (Thai and Sri Lankan languages (at least) are influenced by Pali or use pali words although in some cases the meaning has adapted through time) it is quite feasable to understand what is being said accurately, but the best way to be certain is to study the language itself there are a great many study books and courses which would be of assistance to this!
He who knows only his own side of the case knows little of that. His reasons may be good, and no one may have been able to refute them.
But if he is equally unable to refute the reasons on the opposite side, if he does not so much as know what they are, he has no ground for preferring either opinion …
He must be able to hear them from persons who actually believe them … he must know them in their most plausible and persuasive form.