There is not an "other" feature in normalize. There are a couple of ways you can handle this. One is to use wildards, such as
To represent anything that starts with L and add those to the normalize rule. Or you could create a second Map rule. The map rule has a the Not Found feature that lets you set a value if nothing matching is found. Then you can specify the normalize values in the regular expression value and set the Not Found value to Other.
The second option sounds good to me. I wasn't able to create a mapping to test this. Could you maybe create a test mapping, which you upload here?