"70 languages" Well now you're appealing to Jewish tradition, which I thought you rejected. And of course, there is much more than 70 languages in the world.
Anyway, he did (at one point in time) speak to a few people, to all who came to the foot of a small mountain located at a specific point in space, and perhaps he spoke in multiple languages - then what?
People in - the aforementioned - Oslo and Hong Kong had no idea about this. God could have spoken to everyone ever, every person and generation and nation throughout time, but did not. Never did he speak a word to the Maori or Hawaiians or Eskimoes or Finns or Maasai or Mongols or Teutons or Tibetans, and I could keep going.
" All who came to the foot of the mountain" And how exactly were Eskimoes or the Cherokee or the Vikings or the Chinese supposed to know that there was a mountain in Sinai they were supposed to go to?
To repeat my previous point, God could have sent angels or prophets or spoken by his own voice to any and every people and town and nation and generation throughout time and space but did not. Most people throughout history have never even heard of YHWH, Yeshua (not even the gentilized Kristos), Torah, Moses, or any of these things.