Iconv.iconv('asccii//translit', 'utf-8', 'Těžiště')

ActiveSupport::Multibyte::Unicode.normalize('Těžiště', :kd).chars.grep(/p{^Mn}/).join('')

> UnicodeUtils.compatibility_decomposition('Těžiště').chars.grep(/p{^Mn}/).join('')
 => "Teziste"

def de_accent
    #
    # `p{Mn}` is also known as `p{Nonspacing_Mark}` but only the short
    # and cryptic form is documented.
    #
    ActiveSupport::Multibyte::Unicode.normalize(self, :kd).chars.grep(/p{^Mn}/).join('')
end

> s = 'Těžiště'.de_accent
 => "Teziste"