Hi

I need to build a site that is in two languages on the front end (the back end only in English, the front end English and Irish).

Irish is not a language supported by Joomla language component. I don't need any automatic translation done, as the client will provide tranlations of every article and menu.

Would this product work for this sort of use case? I want the user to be able to click a flag on the home page and get taken to, something like example.com/en or example.com/ir. If I used this on the English version of the site as the master could I create slave site with all the articles copied over as new versions, and then I could put the translations in instead?

I did something like this with WordPress a few years back as the site was multi regional as well as multilingual.

Many thanks,

Yes with JMS, you can create different websites into sub-directories like (/en or /ir)

It is effectivelly possible to create a slave site that is a copy of another one.
So if you decide to clone the "en" website to build the "ir" website, this is absolutely possible.
Once the copy of the website will be done, they will have their content independent.
In other words, if you add an article in the "en" website it will NOT be automatically present in the "IR" website. You will have to copy it manually.