I am a terrrible speller and I always will be. In OS X, I can't live without the spelling suggestions found in the menu when you context click on a word. If this feature was apart of Textastic, it would make writing code so much better. My current workaround consists of copy and pasting the word I think I misspelled into Spotlight, correcting it (if nessacary), and copying it back into my code. It gets extremely annoying when you're doing it all day.
And for 2 or more languages at the same time would be awesome