Specifically, if the pages are not encoded in UTF-8 and use these non-ASCII characters, the tool might show weird characters. This is a confirmed known issue with the tool, and has no impact and your real crawling and ranking in Google.
Using the Google Webmaster Tools Labs feature "Fetch as Googlebot" may show incorrect characters for pages not encoded in UTF-8 that use non-ASCII characters. This is only a display issue in Webmaster Tools and does not reflect how Googlebot actually crawls and indexes content on your pages (which you can verify by viewing the cached page or by searching for keywords within your content). This does not affect your site's crawling, indexing or ranking in our search results.
There is currently no estimated time for when this will be resolved, I assume it is not a huge priority.
Forum discussion at Google Webmaster Help.