I can confirm that the dutch spellchecker works with accented characters now. I have had several crashes this morning, not all repeatable. Some of them I could repeat several times, but then it worked. I will try to explain what happened.
I looked into some older ePUB's (probably not related) which validates fine (i double checked).
Case 1. Search for <a, first by accident RegEx, current file. Then set to Normal, all HTML files. Got a warning that it was in BV. Switched to CV and pressed find next. Crash. Not repeatable.
Case 2. Second crash. Opened the same book, it opens the cover in BV. I change to CV and doubleclick a xhtml file. Crash. Repeatable. From what I see, it appears that Sigil first wants to open it in split view and then changes to CV. It also crashes for other xhtml files.
In case 2 I also tried another ePUB, same story. Then another again after some time and the problem was gone, also for the other ePUB's. Could it be memory related and with regards to opening an xhtml file in split view first? The xhtml files are not big, 30kb tops.
I work on Windows 7 x64 with 4 GB memory.