US: sending international SMS, Hangouts
I'm pretty sure that google hangouts only allows you to receive international text and not send them.  Why I don't know its pretty ridiculous if you ask me.  Here's their support page.  read carefully...
Google Voice Help - Send &amp; receive text messages

You can send and receive text messages using your Google Voice number on the Google Voice website, in the Google Voice app, through your SMS messaging app, or through Hangouts.
International text messages: At this time, Google Voice supports sending text messages to phone numbers in the U.S. and Canada, but you can receive text messages from anywhere in the world. Currently, Google Voice only supports short codes within the U.S.*