That same question was asked on the blog, maybe Dan Stoll‌ may have more information on this?

I think though, it may require a language pack to be available in your farm. But maybe there is another way.

You could use Javascript to translate the values on your buttons and inside your dropdowns.  You could put a css class on your buttons and target them within your Javascript to change their text values.

Another way I could think of off the top of my head would be to potentially create and "hide" these controls in other languages, and make them visible as needed for the selected language.

Either way, this might be a lot of work if you have a lot of terms and/or languages to do this with.  If not, it might not be so bad.

Thanks

The above Link to Dan Stolls NINTEX Forms Blog is no more available?

Any actual best practice solution for mulitlingual Forms