I use windows command line prompt cmd to commit changes with command 
<code>"fossil commit -m "修正问题。"</code>, and then use command <code>"fossil ui"</code> to view the commitment. And find chaos of comments, only after chosing the web page encoding to GBK and the comments seem OK.
I had try following modify and it works fine.
<pre>
src/checkin.c 
========================================
@@ -740,9 +740,11 @@
   blob_appendf(pOut, "Z %b\n", &mcksum);
   if( pnFBcard ) *pnFBcard = nFBcard;
 }
 
-
+#if defined(_WIN32)
+extern char *sqlite3_win32_mbcs_to_utf8(const char*);
+#endif
 /*
 ** COMMAND: ci
 ** COMMAND: commit
 **
@@ -970,8 +972,16 @@
     if( blob_str(&ans)[0]!='y' ){
       fossil_exit(1);
     }
   }else{
+#if defined(_WIN32)
+    char *zConvertComment = sqlite3_win32_mbcs_to_utf8(blob_str(&comment));
+    if (zConvertComment){
+      blob_reset(&comment);
+      blob_append(&comment, zConvertComment, -1);
+      free(zConvertComment);
+    }
+#endif
     db_multi_exec("REPLACE INTO vvar VALUES('ci-comment',%B)", &comment);
     db_end_transaction(0);
     db_begin_transaction();
   }
</pre>