Remove accents from characters

You can try iconv, with the //TRANSLIT (transliteration) option

Ex. given

$ cat file
ë
ê
Ý,text
Ò
É

then

$ iconv -t ASCII//TRANSLIT file
e
e
Y,text
O
E

The GNU recode package is very useful to convert between character encodings, and it has a special case that does exactly this with the "flat" encoding:

recode -f utf8..flat <textin.txt >flattext.out