Wow, the Oscan language had the letter "Я". I thought it exists in cyrillic alphabets only. I know they are different letters having (perhaps) different pronunciation but still. Interesting!
Early Greek thus had not a fixed direction and derivative alphabets such as the Etruscan have settled to one direction of text flow and of letter shapes at random, namely right to left.
Latin has "forked" from the Greek alphabet at another point in time and thus has reversed direction of writing and reverse glyphs with respect to Etruscan and Oscan
After getting used to it it's not that hard to write mirrored text with the opposite hand. It's definitely a lot easier than doing it with the dominant one.
Cyrillic Я is a variant of Old Cyrillic Yys (Ѧ).