Mongo Query condition on third-level attribute

Question

I have a relatively "simple" collection and query requirement.... I need help with the right syntax. :)

Here is the document definition in Java.

public class Entity {
    private String _id = null;
    private String name = null;
    private Map<String, Object> attributes = new Hashmap<String, Object>();
}

Sample data inserted are like

{
    "_id": "pk1",
    "name": "Item 1",
    "attributes": {
        "en": { "attr1": "value 1 in English", "attr2": "value 2 in English"},
        "es": { "attr1": "value 1 in Spanish", "attr2": "value 2 in Spanish"}
    }
}
{
    "_id": "pk2",
    "name": "Item 2",
    "attributes": {
        "en": { "attr1": "value 1 in English", "attr2": "value 2 in English"},
        "ms": { "attr1": "value 1 in Malay", "attr2": "value 2 in Malay"}
    }
}

The language (key) of the map is an example of user provided (thus unpredictable) keys. I want a simple query syntax to be able fetch documents based on the attributes. For example, I want to put in a criteria "'attr1' contains 'value 1'" and query returns both docs, 'Item 1' and 'Item 2'.

Thanks in advance.