The index for SEARCH and CONTAINSSTRING only supports ASCII characters.
It would be helpful to support non-ASCII characters in two ways:
- Just create the index that supports diacritics (this could be expensive/complex)
- Create the index by using a column that transforms diacritics into corresponding ASCII character whenever possible, just as described in Removing diacritics from text in Power Query in Excel and Power BI (crossjoin.co.uk) but without requiring the explicit creation of an additional column with that content. An optional parameter (not enabled by default) in SEARCH and CONTAINSSTRING could activate this behavior.