We're discussing how well each collation SORTS international strings, not whether or not you can store them. There are a lot of instances where you need to be able to store an international string without needing to be able to do a highly accurate ORDER BY on that column.

It's also worth mentioning that by design, UTF-8 doesn't use any more space for storage than ASCII. There are exceptions when databases need to pre-allocate storage, but in general, you should just be using UTF-8 everywhere.