Although it seems that the string “Wallet credit through purchase #” is not translatable through PO file.
So for now I replace the line 107

<p><?php echo $transaction->details; ?></p>

in the file wc-endpoint-wallet.php

for :

<p><?php echo __( ‘Wallet credit through purchase #’, ‘woo-wallet’ ) ?></p>

so now it display the correct translation from po file.

I don’t know if this the correct solution though 🙂