Google Translate is by far one of the best translation apps available for any mobile device, and offers translations in 65 different languages, 24 of which come with speech recognition.
Translation results can be shown full screen when you rotate your phone, which is perfect for showing someone what you are trying to say. The app stores your translation results (and lets you clear them) and you can “star” frequently used translations.
Since all the translation work is done online, you will need a data plan to use – which makes international usage quite expensive. I’d recommend doing text only when you are on roaming data to reduce costs.
The app is free of charge, and can be found on your device in the App Store, or though this link.