[Zope] Pre-indexing filter and accented letters

I would like to index a text property of an object in the ZCatalog. The text is in French language, but I have a problem: I have to find results for the related non accented letters! I mean, If I do a search for "actualite", the index should return also the object which text contains "actualitè". I cannot convert the index to textindexNG, now it is TextIndex (at least, I can covert it to ZCTextIndex). An idea could be, for example, to convert the text before it get indexed... Where should I look in the code? Can it be possible? Any other suggestion? :) TIA!