Why don't we have Star Trek translators?

There is Dragon for english to text. I think I remember something about google having voice to text at some point.

Given how far our technology has advanced (with siri and all that other stuff), why the heck don't we have an app that lets me hold my phone up to a foreign speaker of any of our languages and then read what he/she says? and vice/versa.

Companies could use it... but for travelers even a very rough translation would suffice.