See: http://www.redmine.org/boards/2/topics/31188, also reported in other forum threads and "here":https://github.com/redmine/redmine/pull/6.

The problem is due to the fact that @String#[]@ changed between ruby 1.8 and 1.9. In 1.8 @x[0]@ would return a fixnum representing the character, while it returned the character itself in 1.9 ("1.8 doc":http://ruby-doc.org/core-1.8.7/String.html#method-i-5B-5D, "1.9 doc":http://www.ruby-doc.org/core-1.9.3/String.html#method-i-5B-5D). It's easily explained by the unicode support improvements in 1.9 and the fact that a single 1.9 character can map to multiple codepoints.

The easiest workaround is to let the code as is for 1.8 but only take the first codepoint above (unicode strings can have multiple codepoints per character...).