What are "TCL list elements"? (you wouldn't expect me to go learn about TCL now) I suspect you may need Regexp::Common, as in

use Regexp::Common qw /balanced/;
my( @ek ) = (
"eka toka kolo",
"eka {toka soka} kolo",
"{eka seka leka seka} {toka soka {roka loka moka} doka}{{kolo nolo} {{
+solo molo} tolo} holo rolo}" 
);

for my $str ( @ek ){
    print "$_\n" for $str =~ /$RE{balanced}{-parens=>'{}'}/g;
}
__END__
{toka soka}
{eka seka leka seka}
{toka soka {roka loka moka} doka}
{{kolo nolo} {{solo molo} tolo} holo rolo}
[download]

but that's just a guess.