My experience with Dutch, German and Portuguese, languages that all stay within ISO-8859-1, is that Google is smart enough these days to find pages in any of the fout combinations, of search with or without diacritics / pages with or without diacritics.
I don't know how that is with languages like Rumanian, that need a different ISO-8859 version. (But with Unicode, all of that is obselete.)
Trying some examples from my own page, e.g. Timisoara and Timişoara, Chisinau and Chişinăuetc., confirms my expectation. In both cases, I get results both with and without diacritics. So if you build your pages in the proper spelling, even those who have a good keyboard layout installed (although under Windows, that is easy) and search with ASCII only, you will also be found.