I'm trying to create a filter to allow users to use only English letters (Lowercase & uppercase) and numbers. how can I do that? (ANSI)
(not trying to sanitize, only to tell if a string contain non-english letters)
That filter should get me a clean database with only english usernames, without multibyte and UTF-8 characters.

And can anyone explain to me why echo strlen(À) outputs '2'? it means two bytes right? wans't UTF-8 chars supposed to contain a single byte?

Thanks