How are students supposed to localize them? Is this extension in translatewiki? Can you provide some example commit or link to page that explains the process?
Localizing/translating is not admissible as GCI task. I think you mean i18n'ize... do we really have extensions with hardcoded strings in 2016? O_o
The task description would use some pointer to the files you want the student to perform string extraction on: perhaps https://git.wikimedia.org/blob/mediawiki%2Fextensions%2FMassAction/master/src%2FMassActionSpecialPage.php ? Anything else? The strings also need rewriting in most cases, AFAICT.