Unicode Support

The supported file formats for text files and scripts and their notation in popular editors are shown in this table:

AutoIt Notation	Notepad	Notepad++	SciTE (AutoIt Default Editor)
UTF8 without BOM	ANSI or UTF-8 depending on content (will force a BOM if saved)	UTF-8 without BOM	UTF-8
UTF8 with BOM	UTF-8	UTF-8	UTF-8 with BOM
ANSI	ANSI	ANSI	8 bit / Code Page Property
UTF16 Little Endian	Unicode	UCS-2 Little Endian	UCS-2 Little Endian
UTF16 Little Endian without BOM	Unicode (will force a BOM if saved)	UCS-2 Little Endian without BOM (can't be selected)	Unsupported
UTF16 Big Endian	Unicode big endian	UCS-2 Big Endian	UCS-2 Big Endian
UTF16 Big Endian without BOM	Unsupported	UCS-2 Big Endian without BOM (can't be selected)	Unsupported

The recommended script format is UTF-8 with BOM as that works best with notepad.exe and the AutoIt editor SciTe and guards against scripts unintentionally getting saved in a particular code page.

ANSI formats are not recommended as they can cause problems when run on machines with different locales.

UTF16 BE or LE without a BOM are not recommended. They are widely unsupported. Even with a BOM they are not particularly common and they take up much more disk space than UTF8.

File operations on text files not opened with FileOpen() and explicit unicode flags auto-detect encoding similar to most modern editors. This includes all file functions that are used with a filename, for example FileRead("filename.txt"). Specifically:

Files containing a BOM will be opened in the relevant mode as per that BOM. UTF-8 and UTF-16 BOMs are checked.
UTF-8 and UTF-16 files without a BOM will be automatically detected and opened in the relevant mode.
Files containing nulls are opened in Binary ($FO_BINARY) mode by default (unless they are detected as valid UTF-16). Previously they would be opened in ANSI mode. Use the $FO_ANSI flag to override.
Files containing only characters 1-127 are opened in UTF-8 with no BOM ($FO_UTF8_NOBOM) mode by default. Previously they would be opened in ANSI mode. Use the $FO_ANSI flag to override.
Files containing only characters 1-255 are opened in ANSI ($FO_ANSI) mode by default.
Due to the above FileGetEncoding() now returns 512 ($FO_ANSI) or 256 ($FO_UTF8_NOBOM) instead of 0 which was undocumented but indicated ANSI.

Current Limitations

There are a few parts of AutoIt that don't yet have full Unicode support. These are:

Send and ControlSend - Instead, Use ControlSetText or the Clipboard functions.
Console operations are converted to ANSI.

These limits will be addressed in future versions if possible.