Is this the way to use HibernateCompositeUser type for handling localized contents?
I'm not too familiar with Hibernate, so just some generic notes:


DBMSs usually have case-insensitive attribute names, so a lot of people use underscore to separate words in attribute and table names.


&lt;column name="SHORTDESCRIPTION"/&gt;
&lt;column name="LONGDESCRIPTION"/&gt;



In the case above SHORT_DESCRIPTION and LONG_DESCRIPTION would be easier to read.


Is SQL syntax case sensitive?


    Master_i18n master_i18n=Master_i18n.getInstance();
    master_i18n=dao.getMaster_i18n(rs.getString(arg1[0]), "nl_NL");;



Master_i18n.getInstance() call seems unnecessary, since on the next line the local variable is overwritten. The following is the same (and the first line might not be required at all):

Master_i18n.getInstance();
Master_i18n master_i18n=dao.getMaster_i18n(rs.getString(arg1[0]), "nl_NL");;


&lt;id name="uuid" type="java.lang.String"&gt;



java.lang.String could be simply string here.

public Object nullSafeGet(ResultSet rs, String[] arg1,
        SessionImplementor arg2, Object arg3) throws HibernateException,
        SQLException {

    Master_i18n master_i18n=Master_i18n.getInstance();
    master_i18n=dao.getMaster_i18n(rs.getString(arg1[0]), "nl_NL");;

    //return Master_i18n.getName();
    return Master_i18n;
}



I think currently it does not compile, since return Master_i18n is uppercased Master_i18n which seems a class, not a local variable.

master_i18n=dao.getMaster_i18n(rs.getString(arg1[0]), "nl_NL");;



nl_NL could be a parameter/constant. (Does every caller want to use this locale?) (One of the semicolons is unnecessary at the end of the line.)
I'd use longer and more descriptive variable names than ps, rs, arg1, arg3. Longer names would make the code more readable since readers don't have to decode the abbreviations every time when they read the code and don't have to guess which abbreviation the author uses.

(Clean Code by Robert C. Martin, Avoid Mental Mapping, p25)
Master_i18n is rather an ugly class name. It does not follow the usual CamelCase naming convention.
It also looks like a singleton which is rather an antipattern nowadays. They make testing harder and often hide dependencies which leads to spaghetti code which is really hard to work with. 


What is so bad about singletons?
TotT: Using Dependency Injection to Avoid Singletons
Eliminating static helper classes
The Singleton Pattern