I am a user from Germany and my English isn't perfect. Normally, I use a spell checker (Word) or a translation tool (Google Translate) to check my text. This process isn't comfortable. A translation tool like Google Translate, integrated into the Stack Overflow editor, would be of great value for me.
I am surprised by the critical comments, answers and votes on this request. Therefore I want to clarify the use case for this feature.
Normally I write my text in English. Usually some kind of spellchecking is enabled. If I feel bad about my English I make a machine translation to German. Machine translation isn’t perfect. I know. But if I get totally nonsense in the German translation, there is something wrong with my English, and I iteratively correct this. Next steps: Clipping the text to Stack Overflow's editor, formatting of text and code, send.
I think with this procedure I respect the non-English question policy.
As I initially stated: This isn’t comfortable and it would be much more comfortable with, for example, a mash up, integrating a spell checker and a translation tool.
The question in comments “Doesn't your browser have a spell checker?” - Maybe it’s possible to choose another browser or install further plug-ins, but I prefer a server side solution for this central feature.
The argument “Machine translation leads to poor English” doesn’t apply here. There is no machine translation to English, but just a temporary machine translation to German.