If you want to minimize the number of bugs reported for your web application you should know that codepages are domain of the past. If you want to create multi-language web content all you have to remember is that you should use UTF-8 encoding everywhere
Also if you encounter pages in other encodings you should convert them into UTF8.
What you should know about UTF-8:
Any character can be encoded in UTF-8, converting any other encoding to UTF-8 can be done without loosing data&
UTF-8 is the de facto standard on all internet related protocols.
Any ASCII text is a valid UTF-8 text
UTF-8 is the most simple Unicode encoding and it’s the only one that is not dependent of the byte-ordering.
It’s best to mark UTF-8 as the default encoding for any page you create.
The only real disadvantage I’ve discovered when using UTF-8 encoding is that the encoded text is larger than for some languages like the Asian ones. Still this should be no problem if you enable HTTP compression.
When the usage of UTF-8 can break things
If the text is going to be used on ancient devices that are able to use only 8-bit characters. Like: TV related equipments, or old mobile phones.