Regardless of whether the language is a consequence of the culture (say, they imported it, or had it imposed upon them), how might one determine with accuracy that consistently disciplined speaking (which is preceded by cognition) has no causal dependence on speaking this substantially more strict language itself?
> However, you will not gain this ability or habit just by learning the langauge.
You will not necessarily gain this ability just by learning it, agreed - but using it on a daily basis is another matter.
> In fact, your langauge can even express that same thing today.
It can express it, in some fashion (typically with clumsy, annoying phrases and qualifiers that make people angry, rather than dedicated, socially normal words), but whether one actually does it on a regular basis is another matter.
There are various differences between someone who studied 3 months of 1 hour per week of Jiu Jitsu (or math, physics, etc) classes, and someone who practiced it for several hours a day from an early age.
Even in simple scenarios it can be extremely difficult to accurately predict what the consequences of something are, and language, cognition, and culture are not exactly simple. And, from a scientific/epistemic perspective, one should always keep in mind that an absence of evidence is not proof of absence....which brings to mind another thought experiment that is different but similar: what might a society be like where epistemology and logic are considered crucially valuable skills, and were taught from Grade 1 through 12 to all children, and being incorrect or even speaking epistemically unsoundly were considered seriously shameful? Might it be possible that one would notice anything substantially different in people who were raised in such a culture (and, what might be some differences we might see)? I would be quite shocked if it had no effect.
For example, there are some Australian langauges if I remember correctly where instead of words for left, right, ahead, behind (relative positioning) they use words for something similar to north/south/east/west (absolute positioning) - as in, "give me that cup to your northeast". This of course requires a habit of keeping track of your absolute positioning at all times.
However, you will not gain this ability or habit just by learning the langauge. In fact, your langauge can even express that same thing today. Instead, you will be unable to naturally use their langauge unless and until you get into the habit of keeping track of your absolute positioning.
Similarly, the people growing up in this culture may not easily learn what we mean by left and right, but they would not gain the ability to understand these concepts merely by learning English - instead, they would naturally speak English while avoiding left/right references, or simply make more mistakes than someone growing in a culture where relative positioning is the preferred form of communication.