The following script transforms a utf-8 encoded file with french spécial characters into a plain us.ascii text file without accents on a, e, i, o, u, and c.

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proc remove_accent { line } {
        set result $line
        if {[regsub -all "à" $result "a" match]} {
                set result $match
        }        
        if {[regsub -all "é|è|ê|ë" $result "e" match]} {
                set result $match
        }        
        if {[regsub -all "î|ï" $result "i" match]} {
                set result $match
        }        
        if {[regsub -all "ô|ö" $result "o" match]} {
                set result $match
        }        
        if {[regsub -all "ù|û|ü" $result "u" match]} {
                set result $match
        }        
        if {[regsub -all "ç" $result "c" match]} {
                set result $match
        }        
        return $result
}
        
set inputfile [lindex $argv 0]

set fin [open $inputfile "r"]
set fout [open $inputfile.ascii "w"]
fconfigure $fin -encoding utf-8
fconfigure $fout -encoding ascii 

while {1} {
        set line [gets $fin]
        if [eof $fin] {
                break;
        } else {
                puts $fout [remove_accent $line] 
        }
}
close $fin
close $fout 
======

----
Isn't the following far much quicker?
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string map { "à" "a" "é" "e" "è" "e" "ê" "e" "ë" "e" "î" "i" "ï" "i" "ô" "o" "ö" "o" "ù" "u" "û" "u" "ü" "u" "ç" "c" } $line
======

[AMG]: The double quotes aren't required:

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string map {à a é e è e ê e ë e î i ï i ô o ö o ù u û u ü u ç c} $line
======

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