Created attachment 112193 [details]
screenshot of spelling checker dialogs with no text language selected

Problem description: Spelling checker fails when language changed from English (UK) to Spanish (Mexico)

Steps to reproduce:
1. Default setting for LibreOffice English (UK)
2. Write a document in Spanish. It is full of [English] spelling errors
3. Tools → Language for all text → Spanish (Mexico)

Current behavior:
4. spelling errors are not marked
5. Tools → Spelling and Grammar
6. attached "Spelling" dialog pops up with no text language selected
7. LibreOffice 4.2.7.2 dialog pops up over the "Spelling" dialog: "Continue checking at the beginning of document?"
8. regardless of whether I click Yes or No, both dialogs close, preventing me from setting "Text language"

Expected behavior:
4. the dictionary would be swapped from English (UK) to Spanish (Mexico)
5. misspelled words in Spanish would be marked
6. r-clicking on marked words would pop up a list of candidate replacement words