$ iconv -f UTF-16LE -t UTF-8 myfile.txt | grep pattern

#! /usr/bin/env perl
use strict;
use warnings;
die "3 args are required" if scalar @ARGV != 3;
my $if =$ARGV[0];
my $of =$ARGV[1];
my $pat=$ARGV[2];
open(my $ifh, '<:encoding(UTF-16LE)', $if) or warn "Can't open $if: $!";
open(my $ofh, '>:encoding(UTF-16LE)', $of) or warn "Can't open $of: $!";
while (<$ifh>) { print $ofh $_ if /^$pat/; }

rg pattern filename