they have to be custom written - unless they have been published here, or elsewhere, previously.
check your Private Messaging to download the hook.
you would really need PHP experience to do that, along with knowledge of the database and some WHMCS functions... to get "an" exchange rate is simple enough and is not a million miles away from the thread link I previously gave.
btw, assuming you had a basic hook that passed exchange rates to the template, and wanted to do this in the template using that hook, then to just update only cycle would require...
<span id="recurringMonthly" {if !$totalrecurringmonthly}style="display:none;"{/if}>
<span class="cost">{$totalrecurringmonthly} (₺{($totalrecurringmonthly->toNumeric()*$exchangerate)|string_format:"%.2f"} TL)</span> {$LANG.orderpaymenttermmonthly}<br />
</span>
but don't bother trying that as it wouldn't work without a hook... plus you'd have to update the other 5 recurring cycles in a similar way.... and it would then need many additional IF statements based on how the output is supposed to react to different currencies... I had a quick look at this on Sunday and it would be far more complicated to do this in the template (and even longer to explain) than it would as a hook - and it takes 60 lines of code for the entire hook solution.
you would upload it to the /includes/hooks folder and it should work straight away.
the hook is currently designed to output alternate total recurring pricing in the Order Summary part of viewcart, using the rules that...
if the item(s) in the cart is/are in your default currency (USD I assume), then it will also show the price in your alternate currency (TRY).
if the item(s) in the cart is/are in your alternate currency (TRY I assume), then it will also show the price in your default currency (USD).
if the item(s) in the cart is/are in another currency (e.g EUR), then it will also show the price in your default currency (USD).
I know you only have 2 currencies in your WHMCS install, so that third option should be irrelevant for now.