VBP saves .bld files in UTF-8 [1] encoding (but without a byte order mark [BOM]). Most text editors provide a way to change how they process non-BOM files (to use UTF-8 instead of ANSI or the system code page) or to explicitly specify UTF-8 when opening a file. VBP is also capable of loading UTF-16 [2]encoded .bld files, but it always saves them as UTF-8.
UTF-8 and UTF-16 are two different ways to store (encode) Unicode text, so .bld files are completely Unicode [3].
[1]
http://www.faqs.org/rfcs/rfc3629.html
[2]
http://www.faqs.org/rfcs/rfc2781.html
[3]
http://www.unicode.org/faq/basic_q.html#19