Anyone can fork it and quickly add the i18n (or just translate into a different language) for their own purposes. People will likely want to contribute i18n. People may fix or improve things for you.
Of course, it's entirely up to you - but I've appreciated half-complete software countless times before.
Don't fall into this trap, strike while the HN iron is hot, all these people +1'ing will never come back when you're eventually happy the code quality is "improved"
If it's truly that bad you'll benefit from the feedback since it's an internet exposed service, although considering you're a professional freelancer, I'm sure it's fine.
And yes, I feel like, working on it before open sourcing it is like cleaning before the cleaner. It's ok if the code is messy and there are bugs, that's why OS exist.
Very cool idea imo congrats