Besides GUI, an application has two other parts - Business Logic and Persistence. Typically the Business Logic is isolated and no language changes would be required. For globalized applications, the Persistence is typically a database like Oracle, MySQL, IBM DB2, Microsoft SQL Server etc.
The advancements in Databases Technologies have simplified the support for multi-languages. Most of the databases today support internationalization using Unicode characters. Restrictions on the languages that can be a part of the database can also be imposed. However the availability of this restriction is dependent on the DBMS being used.
Each database management system provides its own procedure to implement this multi-lingual data processing on their database but many times a language parameter setup during installation would suffice.