1. Nighongo.io Turn this into an offline app, should be a lot less in running costs. Otherwise use advertisements. Initially use Google Ads but try to arrange direct-placement advertisements from related businesses (e.g. Japanese language schools, travel agencies to Japan, etc).

2. Try to sell this to enterprises that uses Go and position it as a lint tool for their Go code base.

But if the above failed, move it to a free tier cloud platform (e.g. Heroku's free tier) and just use it as a portfolio to add in your résumé.