JavaScript natively supports the Unicode character set. This means it is multi-byte character aware at the most fundamental level.

Unicode and localization issues are related to one other and the one depends on the other. You cannot effectively localize an environment properly without multi-byte character sets. The extensions to ASCII to make it an international character set were workable but somewhat inconvenient. All manner of escape sequences were required and ultimately, it consumes more space than a multi-byte character would have.

Unicode extended the width of the code points from 8 bits to 16. This allows the character set to increase from 256 to 65536 code points. To all intents and purposes, this is sufficient to encode every glyph and character share required by all languages world-wide.

However, there may still be some limitations in the encoding used for far eastern language variants. These may be addressed in the Unicode version 3.0 standard.