The software includes models of internationalization over the entire world. However, the localization work which has been conducted on Amharic locale development has limitations such as managing Ethiopian calendar and numbers. This has a considerable impact in managing the Amharic locale data in a database as well as in other software systems. Even though there are some researches reporting Amharic locale data is managed by the existing Database Management Systems/DBMS/, the data management way is noticeably exposed to error. However, these kinds of errors are handled in this research by introducing new and appropriate exception handling mechanisms. In this regard, it was not found in the literature review to overcome these problems. In this work, an Amharic Locale Extension module named am_ET was developed to integrate into an open source database environment. The most suitable open-source DBMS PostgreSQL and the C programming language were used. User acceptance testing was conducted to evaluate Amharic locale extension functionalities based on the ISO 9241-11 usability testing attributes, such as user satisfaction, effectiveness and efficiency. To validate it, 35 voluntary potential users were randomly selected to participate in the usability test of the developed system. A descriptive statistical analysis and percentage method had been used to test the collected data. Accordingly, the usability test result showed that a positive opinion for the users and developers to manage Amharic local data as it easily manages data formatted to suit Ethiopian locales system such as currency, calendar, and data/time, reduced costs for developers, and better understanding of product functionalities. Consequently, the developed Amharic locale extension solved problems of data management with Ethiopian locales. The paper found that integrated extension module is helpful in localization and design application areas for all entities that are using Amharic locale in open source databases.