Fairly straightfoward. Define a hash of conversion factors then apply them. Makes no attempt to do correct pluralization because I have no idea what the correct plurals are and little interest in researching them. Conversion factors from Wikipedia: Obsolete Russian units of measurement.
convert(1, 'meter');
say '*' x 40, "\n";
convert(1, 'milia');
sub convert (Real $magnitude, $unit) {
my %factor =
tochka => 0.000254,
liniya => 0.00254,
diuym => 0.0254,
vershok => 0.04445,
piad => 0.1778,
fut => 0.3048,
arshin => 0.7112,
sazhen => 2.1336,
versta => 1066.8,
milia => 7467.6,
centimeter => 0.01,
meter => 1.0,
kilometer => 1000.0,
;
my $meters = $magnitude * %factor{$unit.lc};
say "$magnitude $unit to:\n", '_' x 40;
printf "%10s: %s\n", $_, $meters / %factor{$_} unless $_ eq $unit.lc
for %factor.keys.sort:{ +%factor{$_} }
}