Fix:

CREATE TABLE t1 (s1 CHAR(5) COLLATE latin1_german2_ci);
INSERT INTO t1 VALUES ('Ü');
SELECT FIELD('ue',s1) FROM t1;
The above returned 0 in error.
Now 1 is returned.

mysql-test/r/ctype_latin1_de.result

@@ -278,4 +278,8 @@ s1	COUNT(*)
 SELECT COUNT(DISTINCT s1) FROM t1;
 COUNT(DISTINCT s1)
 1
+SELECT FIELD('ue',s1), FIELD('',s1), s1='ue', s1='' FROM t1;
+FIELD('ue',s1)	FIELD('',s1)	s1='ue'	s1=''
+1	1	1	1
+1	1	1	1
 DROP TABLE t1;

mysql-test/t/ctype_latin1_de.test

@@ -82,4 +82,5 @@ INSERT INTO t1 VALUES ('ue');
 SELECT DISTINCT s1 FROM t1;
 SELECT s1,COUNT(*) FROM t1 GROUP BY s1;
 SELECT COUNT(DISTINCT s1) FROM t1;
+SELECT FIELD('ue',s1), FIELD('',s1), s1='ue', s1='' FROM t1;
 DROP TABLE t1;

sql/item_func.cc

@@ -1183,8 +1183,7 @@ longlong Item_func_field::val_int()
     for (uint i=1 ; i < arg_count ; i++)
     {
       String *tmp_value=args[i]->val_str(&tmp);
-      if (tmp_value && field->length() == tmp_value->length() &&
-	  !sortcmp(field,tmp_value,cmp_collation.collation))
+      if (tmp_value && !sortcmp(field,tmp_value,cmp_collation.collation))
         return (longlong) (i);
     }
   }