Most text encodings are supersets of 7-bit ascii, so in short
yes, valid ascii is also UTF8/16, lantin-1 and most other western
text encodings, but ascii is most valuable as a data-encoding
because it is independent of the endianness of the computer - it
takes less space to store most data in binary, but the bit patterns
for the same data will vary from computer to computer, making the
data less portable