How to translate large string between languages?

I'm currently using GTranslate to do my language translations, but it only seems to accept parameters via the url. If I try to put the text in POST data, the request fails. Obviously, this is a problem for strings greater than a certain length. I could split the string and make lots of requests, but that's terribly inefficient and some context may be lost.

Are there any other translation services out there that allow me to POST large amounts of data to them?

What would be really nice is a translation tool that allows me to upload a json array of all of the things that i need translated at once.

Did you take the server limit in account ?
Most servers are configurated to a max of 1-2 MB for post, and same for upload size.

You could try to upload it to a webserver and use the url from that page as parameter.