Google can almost instantaneously, offer spell correction in every language.
When we search a query, Sometimes we misspell a word on google.
Instead of asking to rewrite the word again, google recorrects the word for us.
Google uses a highly accurate algorithm for that.
It helps us to redirect to correct links directly.
Google uses an interesting ‘spell-checking’ algorithm with a quite high accuracy. Google uses masses of data for Natural Language Processing (NLP). Spelling correction is an application of NLP.
This algorithm needs data preparation from large chunks of data because it evaluates the most used words. It counts the occurrence of each word.
Word searching works by defining the edit distance. Edit distance means how many recent most popular words, related to search, needs to be evaluated. If edit distance is 0-2, then most recent 2 words will be evaluated.
In this way, Google’s ‘showing results for’ or ‘Did you mean’ algorithm works. More you can check here by Spelling corrector implemented and described by Google's Director of Research Peter Norvig.
Watch this video of google wave ( @ 44m 06s ) that shows how google automatically corrects the spelling.