Why dont Jews read/speak lashon hakodesh ("The Holy Language") like the Yeminite Jews whos Hebrew is authentic to the Jews of 2000 years ago
The Hebrew which we speak today, is (!) Lashon HaKodesh and there's no need to break your teeth on the Yemenite accent (although for Kriat Shma, if you want to be stringent...). Check for yourself in any Ben Yehuda or Even Shoshan dictionary and you'll find that more than 90% of the words are from Tanach, Mishna or Talmud. Also, anyone will notice that the Hebrew in the time of Moshe was a little different from that of the Shoftim, which is a little different than that of Yishayau, which is a little different from mishnaic Hebrew, which is a little different from today's. Chazal write that one who speaks Hebrew has a share in the world-to-come (Yerush. Shabbat 1, 3), and they obviously were referring to their Hebrew, even though it's different from Tanachic Hebrew. All spoken languages inevitably evolve, even Chaucer is different from Shakespeare which are both different from today's English. In fact, today's Hebrew actually evolved less than Old French and Old English because it's usually spoken languages that pick up external influences, and Hebrew was studied more than it was spoken. In fact, when Ben-Yehuda had to choose between Tanachic Hebrew and Mishnaic, he usually preferred to "turn the clock" back on evolution, and return as much as possible to the original, so modern Hebrew is davka much closer to her original form, than other languages. In short, the mitzva is to speak Lashon HaKodesh, whichever dialect you prefer (although I suggest to do yourself, and others, a favor and use the common sefaradic dialect which Am Yisrael has accepted- and the "voice of the masses is the voice of G-d"- especially in Am Yisrael!).