Always set language after highlighter creation
Before this patch, the spell-checking language was not set properly after a focusInEvent in a read-write KTextEdit.
createHighlighter() is called in the following scenarios:
- When spell-checking gets enabled (via setCheckSpellingEnabled())
- When there is a focus-in-event
- When we set the text edit to read-write
We always need to (re-)apply the language after a new highlighter is set up in these cases.