A hack: you could edit the strings directly in the *.po file then compile the message file, assuming you’re running your Open edX instance exclusively in Tamil.
This hack won’t be very sustainable as the file will be periodically overwritten by changes upstream.
If you want to submit a pull request, you could mirror examples such as:
If you can’t submit a pull request, this may be a good issue to add to the ecommerce repository. The repository is currently unmaintained and scheduled for deprecation, but it’s good to have this issue documented in case a community maintainer picks up the repository.
It is possible that there is a Tutor-based fix that may be more helpful to you, but as I don’t use Tutor I can’t help you there.