To ensure that accented or non-Western characters sort the way you want them to in the index, you might have to specify a different sort type, or a non-English locale:
[HtmlOptions]
; IndexSortType = Numeric (default, code-point order),
; Lexical (using MS strcoll functions), or
; Alpha (sort accented letters as though they are unaccented).
IndexSortType=Numeric
; IndexSortLocale = language to use for sorting index.
; When IndexSortType is Lexical, default is current
; OS country setting. Uses MS language names.
;IndexSortLocale=English
For example, to make accented letters sort as though unaccented, specify the following:
[HtmlOptions]
IndexSortType = Alpha
Alpha works only with the Windows Western character set and the Unicode character set. Specify Lexical for Central European or Cyrillic locales; Alpha does not handle those. However, DITA2Go does support multibyte sorting when you specify the index locale.
If you use DITA2Go to produce HTML Help in an Asian or Cyrillic language, also specify the Help-file language; see §18.12 Generating HTML Help in non-Western languages.