Yeah this came up ages ago. I think there's something like a 500 character limit with Bing. (I tried to find the original post, but searching here is meh...)
Amber is correct, there's a 500 character limit for translations and unfortunately, this can't be fixed from our side, since it's a limitation from Bing.
I'd recommend translating the whole page from your browser. I use Chrome and it works quite well, and dare I say, faster than the in-built one.
This is ridiculous.
No its not faster using a third party translation. Yet again more extra steps to use this forum.