People count what stands out for them, what has become discrete according to their observations. What stands out depends on the history of the culture and for this reason different cultures will count in different ways. For example, in counting months some cultures count strictly lunar appearances (e.g. the Islamic Calendar), other cultures count months on a strictly solar basis (e.g. the modern Gregorian Calendar and the ancient Egyptian Calendar), and some cultures count months on a mixed solar/lunar relationship (e.g. the Jewish and Chinese Calendars). Every culture counts months, but how months are perceived differs.
Similarly, what constitutes a unit of sound worthy of counting, a syllable, varies from culture to culture. Some cultures count semi-vowels, such as “n”, “m”, and “ng” as syllables while others do not. Japanese counts an “n” as a syllable, but only if it appears at the end, it is not counted if it is an initial sound. Some cultures can have an initial “ng”, counted as a syllable, while in English “ng” is only an ending sound, never initial, and is not counted as a syllable. Some cultures count durations; almost all Sanskrit derived languages have both long and short forms of their vowels so that sometimes the sound “a”, as in “father”, will be counted as one syllable and sometimes two. Japanese also has this aspect of counting syllables with long and short forms of “o” and “a”. Some cultures will count what English speakers would consider a silence as a syllable; as in a glottal stop, or in French poetry where sometimes a silent “e” is counted as a syllable.
In comparing any two languages there are going to be discrepancies over what is considered to be a syllable, just as there are discrepancies among human groups over what is counted when months are counted. This is just a part of the variety of human experience. There’s no logical reason for why certain sounds are counted in one culture, but not in another. It is based on the particular history of that people and their language and just needs to be accepted as how a particular people hears their language; kind of like just accepting irregular verbs or other aspects of a language that one is learning.
The discrepancies in what is counted need not be a barrier for poets. It is the act of counting itself that is shared across cultural lines and it is the act of counting that allows for the transmission of a poetic form from one linguistic context to another. Whatever sounds Japanese count, they are still counting syllables. Whatever sounds English speakers count, they are still counting syllables. The fact that the two groups of sounds do not match is not a problem because the counting itself is shared. It is the counting which is the common ground, a bridge from one culture to another.