How to do this? checking language?

[Rommeo]

I have textfield for signature in my form, I m checking if the signature was sent ( if(!empty($_POST['signature'])) 

and if it's not empty I m putting it into the db.

 

The problem is that, I have noticed a greek user has entered something in greek letters, and function could not deal with it and saved it as it is.( DB field supports greek charset )

 

I just want to allow english and german chars with special chars ( ",',< etc. ) , no other charset like greek.

How can I do that? any function for this purpose ?

[Mahngiel]

I suppose you could use a regular expression to define the permissible characters.  I'm no regex expert, but that's where I'd start the search.